CSLB General Building (B) — All Questions

The California Plumbing Code (Part 5 of Title 24) is republished and adopted on a regular cycle. How often is a new edition normally issued?

• a.Every 3 years✓
• b.Every year
• c.Every 5 years
• d.Only when the Legislature orders it

California adopts its building standards, including the Plumbing Code, on a 3-year cycle (for example the 2019, 2022, and 2025 editions). This matches the model code publication schedule. Contractors must plan work under whichever edition is currently in effect in the jurisdiction.

The California Plumbing Code is adapted from which national model code?

• a.International Plumbing Code (IPC)
• b.Uniform Plumbing Code (UPC)✓
• c.National Standard Plumbing Code
• d.International Residential Code (IRC)

California bases its Plumbing Code on the Uniform Plumbing Code (UPC), published by IAPMO. State agencies then add California amendments. Knowing the source code helps when cross-referencing sections during plan review.

On a set of plumbing drawings, a supply line labeled with the abbreviation "CW" represents which system?

• a.Condensate waste
• b.Chilled water return
• c.Cold water supply✓
• d.Combustion air

"CW" is the standard drawing abbreviation for cold water supply piping; "HW" is used for hot water. Reading these labels correctly is essential to route the right pipe during rough-in. Legends on the plan's first sheet confirm the abbreviations used by that designer.

On plumbing plans, piping that runs below the floor slab or underground is most commonly drawn using which line type?

• a.A double solid line
• b.A line with a row of circles
• c.A heavy solid line
• d.A dashed (broken) line✓

Concealed or below-grade piping is conventionally shown as a dashed line, while exposed or above-slab piping is a solid line. Distinguishing solid from dashed lines tells the installer whether a run is under the slab or overhead. Always confirm against the drawing's line-type legend.

During construction the rough-in (rough) plumbing inspection is generally performed at what point?

• a.After the DWV and water piping are installed but before they are covered or concealed✓
• b.After all fixtures are set and the building is occupied
• c.Before any trenches are dug
• d.Only after the final walk-through with the owner

The rough-in inspection is done once the drain, waste, vent, and water lines are in place and tested but still exposed, so the inspector can view the piping before walls and slabs conceal it. Scheduling it after cover-up would force demolition to inspect. Plan the job so this hold point is met before insulation, drywall, or pour.

For a slab-on-grade house, which sequence of plumbing inspections is correct?

• a.Final, then rough-in, then underground
• b.Underground (groundwork), then rough-in/top-out, then final✓
• c.Rough-in, then underground, then final
• d.Only a single final inspection is required

Work is inspected in the order it is buried or concealed: underground drains under the slab first, then the rough-in/top-out once walls are framed, and finally the trim-out when fixtures are set. Each stage is a hold point that must pass before the next is covered. Sequencing inspections wrong causes failed or missed approvals and rework.

For most commercial plumbing jobs, who is normally responsible for obtaining the plumbing permit before work starts?

• a.The material supplier
• b.The utility company
• c.The licensed contractor performing the work✓
• d.The building inspector

The licensed contractor doing the installation typically pulls the permit and is accountable for the work meeting code. Pulling a permit under the proper license also ties liability to the responsible party. Planning must include permit lead time so inspections can be scheduled on time.

You are doing a material takeoff from an isometric of a bathroom group. The riser drops through one floor and makes three horizontal offsets, each requiring a pair of 90° bends. How many 90° elbows should you count for those offsets alone?

• a.3
• b.4
• c.5
• d.6✓

Each offset uses a pair of 90° bends, and three offsets means 3 × 2 = 6 elbows. Counting fittings directly off the isometric keeps the takeoff accurate. Always tally each fitting type separately so the purchase order matches the drawing.

You are laying out a 2-inch horizontal drainage pipe. What minimum slope does the CPC require for a pipe this size?

• a.1/4 inch per foot✓
• b.1/16 inch per foot
• c.1 inch per foot
• d.1/2 inch per foot

Under CPC Table 708.1, horizontal drainage piping 2½ inches and smaller must slope at least 1/4 inch per foot (about 2%). Larger pipe may be permitted at 1/8 inch per foot. Getting the fall right on the plan prevents solids from settling and clogging the line.CPC 708.1

When planning cleanout locations on a long horizontal building drain, what is the maximum spacing between cleanouts under the CPC?

• a.50 feet
• b.100 feet✓
• c.150 feet
• d.200 feet

CPC 707.4 requires cleanouts on horizontal drainage lines to be spaced not more than 100 feet apart, measured along the developed length of pipe. Additional cleanouts are also required at changes of direction. Locating them on the plan up front avoids code violations and eases future clearing.CPC 707.4

When planning backfill over a drainage pipe laid in a trench, what is the correct practice under the CPC?

• a.Dump large rocks directly on the pipe to save fill
• b.Leave the pipe unsupported and backfill only the ends
• c.Support the pipe on firm bedding for its full length and place backfill so the pipe is not damaged or displaced✓
• d.Backfill only after the final inspection is passed

CPC 314.0 requires piping to be supported on undisturbed or well-compacted material for its full length, with backfill placed in a way that does not damage or move the pipe. Rocks or point loads can crack pipe or create bellies. Proper trench and bedding planning protects the line and preserves the required slope.CPC 314.0

In estimating, a "labor unit" for a plumbing task usually represents what?

• a.The total dollar price charged to the customer
• b.The weight of the fitting in pounds
• c.The number of fittings in a box
• d.The estimated worker-hours to install one item under normal conditions✓

A labor unit is the standard time, usually in worker-hours, to install a given item such as a fixture or fitting under normal job conditions. Estimators multiply counted quantities by labor units to build the labor portion of the bid. Adjustment factors are then applied for job difficulty, height, or congestion.

On a plumbing riser diagram, what does the drawing primarily show?

• a.A vertical, not-to-scale schematic of how piping rises through the floors and connects stacks, branches, and fixtures✓
• b.The exact horizontal dimensions of every pipe on the site
• c.The property survey and lot lines
• d.The electrical panel schedule

A riser diagram is a vertical schematic, usually not to scale, showing how stacks, branches, vents, and fixtures connect from floor to floor. It clarifies the system's vertical relationships that a flat plan view cannot. Estimators use it with the floor plans to count vertical footage and stack fittings.

A plan symbol showing a small circle with a bisecting line and the note "FD" most likely indicates what?

• a.A fire damper
• b.A floor drain✓
• c.A flow detector
• d.A foundation dowel

"FD" on a plumbing plan denotes a floor drain, typically drawn as a small circle at the fixture location. Recognizing fixture abbreviations lets you route waste and vent piping to the correct point. Always verify the abbreviation against the plan's symbol legend, which governs that specific drawing set.

The plan scale is 1/4 inch = 1 foot. A water line measures 5 inches on the drawing. What is the actual pipe length?

• a.5 feet
• b.15 feet
• c.20 feet✓
• d.25 feet

At 1/4 inch = 1 foot, each inch on paper equals 4 feet, so 5 inches × 4 feet = 20 feet. Converting scaled measurements to real lengths is the basis of accurate takeoffs. Double-check the title-block scale before measuring, since sheets in a set can use different scales.

When you coordinate plumbing rough-in with the framing crew, why is it important to review the structural drawings before drilling floor joists?

• a.To find the paint color schedule
• b.To locate the electrical meter
• c.To pick the pipe manufacturer
• d.To confirm allowable hole sizes and locations so you don't compromise the structural members✓

Engineered joists and dimensional lumber have limits on where and how large holes may be, and the structural drawings or manufacturer tables define them. Coordinating before you bore avoids weakening the framing and triggering a red-tag or costly repair. Good trade coordination on paper prevents field conflicts and rework.

You are planning the DWV rough-in test. Under the CPC, a water test of the drainage and vent system is applied so that no section is tested with less than how much head of water?

• a.10 feet of head (except the top 10 feet of the system)✓
• b.1 foot of head
• c.50 feet of head
• d.No head is required; a visual check is enough

CPC 712.0 water test requires the DWV system to be filled so that no section is tested with less than a 10-foot head of water, except for the top 10 feet of the system. This confirms the joints are watertight before concealment. Plan the test at the rough-in stage so any leaks are fixed before cover-up.CPC 712.0

In estimating pipe for a run, why do experienced estimators add a waste/scrap allowance to the measured length?

• a.Because the code requires exactly 25% extra
• b.To account for cutoffs, defects, and field adjustments so the job does not run short✓
• c.To inflate the price with no reason
• d.Because pipe is sold only by the ton

Real installations lose material to cutoffs, damaged ends, and field changes, so a small percentage is added so the crew does not run out mid-job. The allowance is a planning judgment, not a fixed code number. Too little risks shortages; too much wastes money, so estimators base it on the pipe type and job conditions.

On the plans a valve symbol drawn as two triangles meeting point-to-point (a bowtie) most commonly represents which device?

• a.A pipe hanger
• b.A cleanout
• c.A gate or general shutoff valve✓
• d.A floor sink

The bowtie of two triangles meeting at their points is the standard schematic symbol for a valve, commonly a gate or general shutoff valve, with added marks distinguishing specific types. Reading valve symbols lets you count and locate shutoffs during takeoff. The plan's legend defines which valve type each variation means.

A restaurant plan calls for eight identical mop-sink rough-ins. Each rough-in needs 1 P-trap, 1 trap adapter, and 2 drop-ear elbows. How many drop-ear elbows go on the takeoff?

• a.8
• b.10
• c.12
• d.16✓

Two drop-ear elbows per rough-in times eight rough-ins equals 2 × 8 = 16. When many identical assemblies repeat, multiply the per-unit fitting count by the quantity. Building a per-assembly parts list first makes repetitive takeoffs fast and accurate.

While laying out the building drain you reach a 90° change of direction. Under the CPC, what feature is generally required at such a change of direction on the horizontal drain?

• a.A cleanout✓
• b.A pressure-reducing valve
• c.A backwater vent only
• d.An expansion tank

CPC 707.0 requires cleanouts at changes of direction greater than 45 degrees in horizontal drainage piping so the line can be rodded from that point. Planning the cleanout into the layout keeps the run serviceable. Missing a required cleanout is a common cause of failed rough-in inspections.CPC 707.0

What is the main purpose of a plumbing fixture schedule on a set of plans?

• a.To list the paint finishes
• b.To identify each fixture type, its connection sizes, and its mark so it can be matched to the floor plan✓
• c.To show soil-bearing capacity
• d.To give the electrical load calculations

A fixture schedule lists each fixture by mark or tag along with its make/model reference and connection sizes, letting the installer match plan symbols to real fixtures. It drives both the material order and the rough-in dimensions. Reading it alongside the floor plan avoids ordering the wrong fixture or trap size.

When sizing the water distribution system for a building, which CPC-recognized method bases pipe sizes on total demand expressed in water supply fixture units and available pressure?

• a.Counting only the number of rooms
• b.Matching the sewer pipe size
• c.The fixture-unit sizing method using the code's sizing tables✓
• d.Using the same size as the gas piping

CPC 610.0 sizes water piping using water supply fixture units (WSFU), developed length, and available pressure applied to the code's sizing tables. This translates fixture demand into required pipe diameters. Choosing the correct sizing method on the plan ensures adequate flow without oversizing.CPC 610.0

You must coordinate a 4-inch sanitary line and an HVAC duct that cross in a tight ceiling. What is the best planning step to resolve the conflict before installation?

• a.Install whichever trade arrives first and let the other adjust
• b.Cut the duct on site without telling anyone
• c.Ignore it since pipes always win
• d.Compare the trades' drawings (or a coordination/BIM model) to reroute one system and preserve required clearances and drain slope✓

Overlaying the plumbing, mechanical, and structural drawings, or a coordination model, reveals clashes so one system can be rerouted on paper. The drain must keep its required slope, so it usually sets the elevation and the flexible duct moves. Resolving clashes before installation avoids demolition and schedule delays.

What does the term "top-out" refer to during the phases of a plumbing installation?

• a.Completing the DWV and water piping through the walls and stubbing out for fixtures, ready for the rough inspection✓
• b.The final cleanup at the end of the job
• c.Setting the water heater temperature
• d.Pouring the foundation footings

Top-out is the phase where the drain, waste, vent, and water lines are run up through the framed walls and stubbed out for fixtures, completed for the rough inspection. It follows the underground work and precedes trim-out. Planning materials by phase, underground then top-out then trim, keeps the crew supplied at each stage.

On a plumbing plan you see three parallel lines each with a different break symbol: a single dash, a dash-dot, and a solid. What is the best way to know which system each represents?

• a.Assume the solid line is always gas
• b.Read the line-type legend on the plan set✓
• c.Guess based on pipe size
• d.Call the fixture manufacturer

Different designers assign line types to systems (waste, vent, water, gas) in the legend, so the legend is the authoritative key for that set. Guessing risks routing the wrong pipe. Always confirm line types and abbreviations against the specific drawing's legend before takeoff or layout.

An estimator prices a job at 2 fixtures' rough-in per hour and there are 40 fixtures. If the labor rate is $60/hour, what is the estimated rough-in labor cost?

• a.$600
• b.$800
• c.$1,200✓
• d.$2,400

At 2 fixtures per hour, 40 fixtures take 20 hours; 20 hours × $60 = $1,200. Converting fixture counts to hours to dollars is the core of labor estimating. Keep production rates and labor rates separate so either can be adjusted without redoing the whole estimate.

Why should you check which edition of the California Plumbing Code the local jurisdiction has adopted before finalizing a design?

• a.Editions never change any requirements
• b.Only the fixture colors change between editions
• c.The state prohibits using any local amendments
• d.Requirements can change between editions and local amendments may add stricter rules that affect the design✓

Each 3-year edition can revise requirements, and local jurisdictions may adopt amendments that are stricter than the state minimum. Designing to an outdated edition or ignoring local amendments risks plan-check rejection. Confirming the adopted edition and amendments up front keeps the design compliant.

In a plumbing isometric drawing, pipes are drawn at what angle to represent the three dimensions on a flat sheet?

• a.Typically at 30-degree angles to show horizontal runs, with verticals drawn straight up✓
• b.All lines at 90 degrees only
• c.Random angles chosen by the drafter
• d.Curved lines throughout

Plumbing isometrics conventionally draw horizontal piping at 30-degree angles and vertical piping straight up, giving a 3-D view on a 2-D sheet. This lets you see rises, drops, and offsets that a plan view flattens. Reading isometrics correctly is essential for counting vertical fittings and understanding connection order.

When planning a trench for a building sewer, what does the CPC require regarding the bottom of the trench?

• a.It may contain sharp rocks as long as the pipe is strong
• b.The pipe must rest on a firm bed for its entire length, with bell holes provided at joints✓
• c.The trench must be filled with water first
• d.The bottom can slope backward toward the building

CPC 313.0 requires piping to be laid on a firm bed throughout its length, with bell holes excavated at joints so the barrel bears evenly. Point loading on rocks or unexcavated bell holes can crack pipe or throw off the slope. Planning proper bedding protects the line and keeps the required fall to the main.2022 California Plumbing Code (CPC) §314.0

A plan note reads "See detail 3/P-4." What does this callout tell the installer?

• a.To pour 3 inches of concrete
• b.That there are 4 pipes at this location
• c.To look at detail number 3 on sheet P-4 for an enlarged view of that connection✓
• d.That the pipe is 34 inches long

A callout like "3/P-4" points to detail number 3 on drawing sheet P-4, where a larger-scale view shows the connection specifics. Following detail references prevents guessing at how a joint or assembly is built. Cross-referencing details is a normal part of reading a full plan set.

Before excavating a trench for underground plumbing on a commercial site, which coordination step is most important for safety and to avoid utility strikes?

• a.Order the fixtures
• b.Set the water heater
• c.Paint the walls
• d.Have underground utilities located/marked (call the one-call center) and review the site utility plan✓

Contacting the regional one-call center to mark existing utilities, and reviewing the site utility plan, prevents striking gas, electric, or communication lines during excavation. This is both a safety requirement and a coordination step with other trades and utility owners. Locating utilities first avoids injury, outages, and costly repairs.

When sizing a building sewer during layout, the required size is based primarily on what?

• a.The total drainage fixture units carried and the slope, per the code's sizing table✓
• b.The color of the fixtures
• c.The number of electrical outlets
• d.The height of the roof

CPC 718.0 and its referenced tables size the building sewer from the total drainage fixture unit (DFU) load it carries at a given slope. More fixture units or a flatter slope require a larger pipe. Sizing from DFUs on the plan ensures the sewer can carry peak flow without surcharging.CPC 718.0

What is the main reason to prepare a written material takeoff before ordering pipe and fittings for a job?

• a.To satisfy the painter
• b.To order accurate quantities so the crew avoids shortages and costly return trips✓
• c.To replace the need for any plans
• d.To set the water pressure

A written takeoff converts the drawings into a counted list of pipe, fittings, valves, and fixtures so the order matches the job. Accurate quantities prevent both shortages that stall the crew and over-ordering that ties up money. It also becomes the basis for the material portion of the estimate.

When laying out vent piping, the CPC requires vents to be graded and connected so they do what?

• a.Trap water at every low point
• b.Run perfectly level with no slope
• c.Drain back by gravity to a soil or waste pipe so condensate cannot collect✓
• d.Terminate below the flood-level rim of a fixture

CPC 906.0 requires vent pipes to be graded and connected to drain back by gravity to a soil or waste pipe, preventing condensate or rainwater from collecting and blocking the vent. A vent that sags and holds water can lose its function. Planning the vent slope and connection points keeps the venting system self-draining.CPC 906.0

You take off 220 linear feet of pipe from the plans and add a 10% waste allowance. Pipe is stocked in 20-foot lengths. How many 20-foot lengths should you order?

• a.11
• b.12
• c.13
• d.13 (242 feet rounded up)✓

220 feet plus 10% is 242 feet; dividing by 20 gives 12.1 lengths, which rounds up to 13 whole sticks. You must round up to whole stock lengths since pipe is sold by the stick. Rounding up prevents ending a run one coupling short on install day.

During planning, what is the purpose of a plumbing "plot" or "site" plan as opposed to the floor plan?

• a.It shows the building's location on the lot and the routes of underground water, sewer, and gas services to the mains✓
• b.It shows the color of interior finishes
• c.It shows only the roof framing
• d.It lists the furniture layout

A site or plot plan shows the building footprint on the property and the underground service routes, points of connection, and utility easements to the public mains. It is essential for planning the sewer and water service excavation and for coordinating with the utility. The interior floor plan, by contrast, details the piping within the building.

When exactly is the final plumbing inspection normally performed?

• a.Before the underground piping is covered
• b.After all fixtures and appurtenances are installed and the system is complete and operational✓
• c.Halfway through the rough-in
• d.Before the permit is issued

The final inspection occurs when all fixtures, trim, and appurtenances are set and the system is fully operational, so the inspector can verify complete, code-compliant work and proper function. It follows the underground and rough-in approvals. Scheduling it too early, before fixtures are set, results in an incomplete inspection and a re-inspection fee.

On a gas piping plan, a note reads "2 PSI system." For planning, what does this primarily affect?

• a.The paint on the pipe
• b.The fixture color
• c.The pipe sizing and the need for a line regulator, since higher delivery pressure changes the sizing method✓
• d.The roof slope

A 2 psi gas delivery pressure lets smaller pipe carry the same load but requires a line pressure regulator downstream to drop to appliance pressure, and the sizing tables differ from a standard low-pressure system. Recognizing the system pressure on the plan drives correct pipe sizing and regulator placement. Using the wrong sizing basis under-sizes or over-sizes the gas main.

A two-story building has identical bathroom stacks on floors 1 and 2. The floor-to-floor height is 10 feet. Estimating vertical pipe for one stack from the first-floor drain to the second-floor branch, roughly how much vertical footage should you count?

• a.2 feet
• b.4 feet
• c.6 feet
• d.About 10 feet plus fitting takeout✓

The vertical run between floors equals the floor-to-floor height, about 10 feet, adjusted for fitting takeout and stub heights. Reading the section or riser diagram gives the vertical dimension the plan view cannot. Counting vertical footage per floor and multiplying by the number of floors builds an accurate stack estimate.

A plan symbol shows a circle with the letters "CO" next to a drain line at grade. What does this indicate?

• a.A cleanout at that location✓
• b.A carbon-monoxide alarm
• c.A cold-only faucet
• d.A concrete opening

"CO" on a drainage line marks a cleanout, an access fitting for rodding the line. Recognizing the cleanout symbol lets you count them for the takeoff and verify code-required locations. Confirm the abbreviation on the plan legend, since "CO" can mean different things on other discipline drawings.

Why do estimators apply a difficulty or productivity factor to base labor units on some jobs?

• a.Because base labor units already include all overhead and profit
• b.Because real conditions like high ceilings, congestion, or occupied buildings slow production compared to ideal conditions✓
• c.Because the code sets the factor at 2.0 for all work
• d.Because material cost changes the labor unit directly

Base labor units assume normal working conditions, so factors adjust them upward for tough conditions such as working overhead, in tight spaces, or in an occupied building. Applying a realistic factor keeps the labor estimate from being too low. Underestimating labor is a leading cause of jobs losing money.

On a plumbing plan, what does a "point of connection" (POC) note typically identify?

• a.The color of the fixture
• b.The paint booth location
• c.Where the new piping ties into an existing system or the public utility main✓
• d.The parking count

A point of connection marks where new work ties into an existing pipe or the public main, defining the boundary of the contractor's scope. Locating the POC is critical for planning excavation, permits, and coordination with the utility. Missing or misreading the POC can leave a gap between new and existing systems.

When must a plumbing permit generally be obtained relative to starting the work?

• a.Any time within a year after finishing
• b.Only if an inspector happens to visit
• c.After the final inspection
• d.Before the work covered by the permit begins✓

A permit must be secured before starting the regulated work, since it authorizes the installation and sets up the required inspections. Beginning work without a permit can lead to stop-work orders, fines, and forced exposure of concealed work. Plan the permit into the schedule so it is in hand before the crew mobilizes.

A single-line water piping diagram on the plans is best described as what?

• a.A schematic showing each pipe as one line with sizes and connections, not the actual physical thickness or exact routing✓
• b.A full-scale drawing showing true pipe diameters
• c.A photo of the finished job
• d.The manufacturer's warranty

A single-line diagram represents each pipe as a single line annotated with size and connections, conveying system logic rather than physical scale. It is quick to read for sizing and routing intent but must be combined with the scaled plans for exact locations. Estimators use it to trace the system and pick up sizes for the takeoff.

When planning the drainage layout, why must roof and storm drainage generally be kept separate from the sanitary drainage system?

• a.Because storm water is warmer
• b.Because the code requires storm drainage to be an independent system, not discharged into the sanitary sewer, unless specifically approved by the authority✓
• c.Because storm pipe is always larger than 12 inches
• d.Because sanitary pipe cannot be plastic

CPC 1101.0 and related sections require storm drainage to be conveyed by an independent system rather than combined with sanitary drainage, except where a combined system is specifically approved. Mixing them can overload the sanitary sewer and treatment system during rain. Planning separate systems on the drawings keeps the layout compliant.CPC 1101.0

A bid schedule shows the plumbing rough-in must be complete before the concrete slab is poured. What does this tell you about coordination?

• a.Plumbing can start any time
• b.The concrete crew controls the plumbing design
• c.The underground plumbing is a predecessor task that must finish and pass inspection before the slab pour, so it must be scheduled and inspected first✓
• d.The slab pour has no effect on plumbing

The underground plumbing is a predecessor to the slab; it must be installed, tested, and inspected before concrete covers it. Coordinating with the concrete crew and inspector so the underground passes on time keeps the pour on schedule. Missing this window forces either a delay or breaking the slab later.

Under the CPC, what is the general purpose of requiring a permit and inspections for plumbing work?

• a.To increase the contractor's profit
• b.To choose the fixture brand
• c.To schedule the painters
• d.To ensure the installation is reviewed and inspected for conformance with the code before it is placed in service✓

CPC 103.0 provides for permits and inspections so that regulated plumbing work is reviewed and verified to conform with the code before use. This protects public health and safety by confirming the system is installed correctly. Planning for required permits and inspection hold points is part of every compliant job.CPC 103.0

You are counting fixtures for a two-bathroom house: each bathroom has 1 water closet, 1 lavatory, and 1 shower, and the kitchen has 1 sink. How many fixtures go on the rough-in count?

• a.7✓
• b.6
• c.8
• d.9

Two bathrooms at 3 fixtures each is 6, plus the 1 kitchen sink, for a total of 7 fixtures. A clean fixture count drives both the material takeoff and the labor units for rough-in and trim. List each room's fixtures separately so nothing is missed when summing the job.

During planning, what is the main reason to record the invert elevation of the sewer point of connection before designing the underground drainage?

• a.To pick the fixture color
• b.To confirm there is enough fall from the building's lowest fixture to the connection so gravity drainage will work✓
• c.To size the electrical service
• d.To choose the paint

The invert elevation is the inside-bottom level of the pipe at the connection; comparing it to the building's lowest fixture confirms there is adequate fall for gravity drainage at the required slope. If the fall is insufficient, the plan may need a sewage ejector or a redesign. Verifying invert and slope up front prevents a system that cannot drain by gravity.