CSLB Trade — Plumbing (C-36) — All Questions
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360 questions
Where a vent penetrates the roof, the plumber must provide…
- a.a pressure-reducing valve
- b.a cleanout at the roof
- c.a backwater valve
- d.a flashing (jacket) to make the roof penetration watertight✓
Every vent that passes through the roof must be made watertight with a proper flashing or roof jacket. Without it, rainwater would leak into the structure around the pipe. The flashing is sealed to both the roofing and the vent pipe.
A sewage sump that receives water-closet discharge and is served by a pump must be provided with a vent that…
- a.connects to the pump discharge line
- b.may be omitted if the pump is sealed
- c.is 1/2 inch minimum
- d.is sized per code and connects to the building vent system or extends independently to open air✓
A sealed sewage sump requires a vent, sized per code, that either ties into the building vent system or runs independently to the outside. The vent equalizes pressure as the sump fills and the pump discharges, and releases sewer gas outdoors. It must never connect to the pump discharge or be omitted.2022 California Plumbing Code (CPC) §710.0
For a building where sewage must be pumped and continuity of service is essential (such as public use), the CPC generally requires…
- a.a single large pump only
- b.no pump, only a holding tank
- c.a gravity bypass to the roof
- d.duplex (two) pumps or ejectors so one can operate if the other fails✓
Where interruption of pumping would create a health hazard, such as buildings used by the public, duplex pumps are required so that a standby unit takes over if one fails. The pumps typically alternate and can run together during peak flow. A single pump risks a sewage backup during any failure.2022 California Plumbing Code (CPC) §710.0
Sub-soil drains, foundation drains, and other clear-water drainage collected below sewer level should discharge to…
- a.the vent stack
- b.a separate sump that pumps clear water to an approved point of disposal, kept separate from sewage✓
- c.a grease interceptor
- d.the sanitary sewer directly
Clear-water drainage such as foundation and sub-soil drains must be collected in its own sump and pumped to an approved disposal point, not mixed with sanitary sewage. This avoids overloading the sanitary system with ground water and keeps a clean-water pump from handling sewage. The clear-water sump does not need to be gastight like a sewage sump.2022 California Plumbing Code (CPC) §710.0
An interior rainwater leader (a vertical storm pipe that carries storm water through a building) must be…
- a.vented like a sanitary stack
- b.connected to the sanitary building drain
- c.installed and, where it connects to a horizontal storm drain, sized to handle the roof area served✓
- d.trapped with a grease interceptor
An interior rainwater leader (conductor) must be sized for the roof area it drains and connected to a properly sized horizontal storm drain, kept separate from sanitary piping. Because storm systems carry no sewage, they are not vented like sanitary stacks, though offsets and connections still follow the storm-drainage rules. Where a leader could receive sewer gas, a trap is required.2022 California Plumbing Code (CPC) §1101.0
When a primary roof drain could become blocked and allow water to pond on the roof, the code requires…
- a.a backwater valve on the roof drain
- b.a secondary (overflow) roof drainage system or scuppers with independent discharge✓
- c.no additional provision
- d.a larger sanitary vent
Roofs must have a secondary (overflow) drainage system, such as overflow drains or scuppers, in case the primary roof drains clog. The overflow discharges independently so that a blockage does not let water accumulate to a structurally dangerous depth. This protects the roof structure from collapse under ponding loads.2022 California Plumbing Code (CPC) §1101.0
A hydromechanical grease interceptor is typically installed…
- a.after the building trap
- b.on the vent line
- c.as close as practical to the fixtures served, with a flow-control device limiting flow to its rated GPM✓
- d.inside the water closet
A hydromechanical grease interceptor should be located as close as practical to the fixtures it serves so grease is captured before it cools and adheres to piping. A flow-control fitting restricts flow to the unit's rated GPM, giving grease time to separate. It must remain accessible for regular cleaning.2022 California Plumbing Code (CPC) §1014.0
A small under-the-sink hydromechanical grease trap rated to PDI standards commonly has a flow rating such as…
- a.5 GPM
- b.20 or 25 GPM with a matching grease capacity✓
- c.100 GPM
- d.500 GPM
Point-of-use grease traps are commonly rated at low flows such as 20 or 25 GPM, matched to a corresponding grease-retention capacity in pounds. A flow-control fitting holds the flow at that rating so grease can separate. Larger loads require larger hydromechanical units or a gravity interceptor.2022 California Plumbing Code (CPC) §1014.0
An indirect-waste standpipe receiving a domestic clothes washer must have a trap, and the standpipe height above the trap weir must generally be within what range?
- a.12 to 16 inches
- b.6 to 12 inches
- c.36 to 48 inches
- d.18 to 30 inches (457–762 mm)✓
A clothes-washer standpipe must be trapped and vented, and the standpipe usually extends between 18 and 30 inches above the trap weir. Too short a standpipe can overflow during the wash pump-out; too tall creates back-pressure and slow draining. The trap is set at an accessible height below the standpipe.2022 California Plumbing Code (CPC) §804.0
What distinguishes an 'air break' from an 'air gap' in an indirect waste installation?
- a.An air break lets the indirect pipe terminate below the receptor's flood-level rim (the pipe may touch the receptor), while an air gap keeps a physical separation above the flood-level rim✓
- b.They are identical terms
- c.An air gap allows the indirect pipe to be submerged
- d.An air break always has a larger separation than an air gap
An air gap is an unobstructed vertical separation above the flood-level rim of the receptor, giving full protection against back-siphonage. An air break allows the indirect drain to end below the flood-level rim, even touching the receptor, but not submerged. Higher-hazard equipment (like food equipment) requires the full air gap, while lower-hazard drains may use an air break.2022 California Plumbing Code (CPC) §801.0
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A combination waste-and-vent system is chiefly intended for…
- a.floor drains, sinks, and similar fixtures where conventional venting is impractical, using oversized horizontal piping✓
- b.water-heater relief piping
- c.roof (storm) drainage
- d.a battery of water closets
A combination waste-and-vent system uses oversized horizontal drain piping that carries both waste and air, providing venting for fixtures like floor drains and sinks in large open areas where a conventional vent cannot be run. Water closets and other high-discharge fixtures are generally not permitted on this system. The oversized pipe flows only partially full so air can move above the waste.2022 California Plumbing Code (CPC) §910.0
As a vent extends upward toward its terminal, its required diameter…
- a.may be reduced by half at the roof
- b.may be reduced to 1/2 inch above the roof
- c.must double at every branch
- d.must not be reduced (no decrease in size in the direction of the terminal)✓
A vent may not be reduced in size in the direction of flow toward the outlet; the required diameter is maintained or increased, never decreased, up to the terminal. Reducing the vent would restrict airflow and could allow frost or debris to close it. This is separate from the frost-closure rule that enlarges the terminal in cold climates.
Two fixtures set on the same floor level and connecting to a common vertical drain within the required distance may share…
- a.a common vent, provided the drain and vent are sized for both fixtures✓
- b.one cleanout only
- c.a single trap for both
- d.one backwater valve
Two fixtures at the same level connecting to a shared vertical drain within the code distance may be served by a common vent, with the connecting drain and vent sized for the combined load. Each fixture still has its own trap; a single trap serving two fixtures is generally prohibited. Common venting saves piping for back-to-back layouts.
Where a building (house) trap is installed on the building drain, it is commonly accompanied by…
- a.a sump pump
- b.a grease interceptor
- c.a fresh-air inlet on the upstream (building) side to ventilate the drainage system✓
- d.a backwater valve on the vent
A building (house) trap isolates the building drainage from the public sewer, and when used it is paired with a fresh-air inlet on the building side so the drainage system stays ventilated. Because a house trap can collect debris and block flow, many modern codes discourage or prohibit it. The fresh-air inlet terminates in open air, screened against pests.
In a horizontal wet-vent system, how must the wet-vented pipe (which carries both waste and air) be sized?
- a.at 4 inches regardless of load
- b.at 1-1/4 inch minimum only
- c.the same as the smallest fixture drain
- d.Per the DFU load of the wet-vented section, and at least 2 inches where a water closet drains through it✓
The wet-vented pipe must be sized for the drainage fixture unit (DFU) load of the fixtures it serves, and must be at least 2 inches where a water closet discharges into it. Adequate size keeps the pipe partially full so air can pass above the waste to vent the group. Undersizing would let the pipe flow full and lose its venting action.2022 California Plumbing Code (CPC) §908.0
A temperature-and-pressure (T&P) relief valve on a residential storage water heater must be set to open at a temperature no higher than which value?
- a.150°F
- b.210°F✓
- c.180°F
- d.240°F
A T&P relief valve protects the tank against overheating and must be rated so its temperature element opens at no more than 210°F. The pressure element is a separate rating. Both must be listed and approved for the appliance.2022 California Plumbing Code (CPC) §608.3
The pressure element of a water heater T&P relief valve must be set to open at a pressure not exceeding which value?
- a.75 psi
- b.150 psi✓
- c.200 psi
- d.100 psi
The pressure portion of a listed T&P valve on a domestic water heater is limited to open at no more than 150 psi. This protects the tank, which is typically rated at 150 psi working pressure. Using a higher setting is prohibited.2022 California Plumbing Code (CPC) §608.3
The discharge pipe served by a water heater T&P relief valve must be sized so that it is:
- a.not smaller than the diameter of the valve outlet✓
- b.one pipe size smaller than the valve outlet
- c.sized for the water heater inlet
- d.always 3/4 inch regardless of the valve
The relief discharge pipe must be at least the full size of the T&P valve outlet, with no reduction along its length. Reducing the pipe would restrict flow during a discharge event and defeat the safety function. It must also serve only one relief valve.2022 California Plumbing Code (CPC) §608.5
A T&P relief valve discharge pipe terminating outside the building must end how far above the ground or receptor?
- a.between 24 and 48 inches
- b.flush with the ground
- c.not less than 6 inches and not more than 24 inches✓
- d.at least 36 inches above grade
The end of the discharge pipe must terminate not less than 6 inches and not more than 24 inches above its point of discharge, such as grade or a receptor. This keeps hot water from spraying an occupant while keeping the outlet visible and above flooding. The end must remain unthreaded and point downward.2022 California Plumbing Code (CPC) §608.5
Which condition is required at the terminal end of a water heater relief valve discharge pipe?
- a.It must not be threaded✓
- b.It must have a threaded cap
- c.It must contain a trap
- d.It must include a shutoff valve
The end of a relief discharge line must not be threaded so it cannot be capped or plugged, which would disable the relief path. No valve or trap may be installed in the line. The pipe must drain by gravity and point downward.2022 California Plumbing Code (CPC) §608.5
A plumber is routing the discharge from a water heater T&P valve. Which installation is code-compliant?
- a.Trap the line to catch drips before it exits
- b.Run the pipe full-size with no valve between the T&P valve and the outlet✓
- c.Reduce the pipe to 1/2 inch to fit through the wall
- d.Install a ball valve in the line for easy testing
No shutoff or check valve may be placed between the relief valve and the discharge outlet, because a closed valve would block emergency relief. The pipe stays full-size and untrapped, draining by gravity to an approved point. These rules keep the safety discharge always open.2022 California Plumbing Code (CPC) §608.5
How must a water heater relief valve discharge pipe flow to its point of discharge?
- a.Uphill to an overhead receptor
- b.Level with no slope
- c.Through a pump to grade
- d.Downward, draining by gravity✓
The discharge pipe must run downward from the valve so it drains completely by gravity to the point of discharge. Any low spot, trap, or upward run could hold water and freeze or block the line. Continuous fall keeps the relief path clear.2022 California Plumbing Code (CPC) §608.5
The material used for a water heater T&P relief valve discharge pipe must be:
- a.any flexible plastic tubing on hand
- b.cast iron for durability
- c.copper only, never plastic
- d.rated for the temperature and pressure of the relief discharge✓
The discharge pipe material must be listed and rated to handle the hot water and pressure that a relief event produces. Ordinary low-temperature tubing can soften or fail. Approved materials include those permitted for hot-water distribution, such as CPVC or copper.2022 California Plumbing Code (CPC) §608.5
When a T&P relief discharge terminates to an indoor location such as a floor drain or pan, an air gap is required. Where must that air gap be located?
- a.Inside the water heater tank
- b.At the point of discharge, so the pipe does not connect directly to a drain✓
- c.Only at the water heater cold inlet
- d.At the gas control valve
The relief discharge must terminate through an air gap at the receptor so it is never directly connected to the drainage system. A direct connection could siphon sewer gases or block discharge. The air gap keeps the relief outlet open to atmosphere and visible.2022 California Plumbing Code (CPC) §608.5
Which of the following is prohibited on a water heater relief valve discharge line?
- a.Installing a trap in the line✓
- b.Running it to the outside of the building
- c.Sizing it full to the valve outlet
- d.Using CPVC rated for hot water
A trap must never be installed in a relief discharge line because standing water could freeze or block the emergency path. The line must drain freely by gravity with no valves or traps. It may terminate outside or to an approved receptor with an air gap.2022 California Plumbing Code (CPC) §608.5
California requires storage water heaters to be braced against earthquakes. What is the minimum number of straps required?
- a.Two straps, one in the upper third and one in the lower third✓
- b.One strap at the top
- c.One strap at the center
- d.Four straps evenly spaced
Water heaters must be anchored with at least two straps to resist horizontal displacement in a seismic event. One strap is placed in the upper one-third of the tank and one in the lower one-third. This keeps the tank from toppling and shearing its gas or water connections.2022 California Plumbing Code (CPC) §507.2
When strapping a gas water heater, the lower seismic strap must be located:
- a.at the very bottom of the tank base
- b.directly over the gas control valve
- c.anywhere below the midpoint
- d.at least 4 inches above the controls✓
The lower strap must be positioned no lower than 4 inches above the gas controls so the strap does not interfere with or damage the control valve. The upper strap goes in the upper third of the tank. Both straps anchor the tank to the wall framing.2022 California Plumbing Code (CPC) §507.2
Seismic straps for a water heater must be anchored to what?
- a.The relief valve discharge pipe
- b.The finished drywall surface only
- c.The wall studs or structural framing✓
- d.The flexible gas connector
The straps must be secured into structural framing such as wall studs, not just the drywall, so they can resist the tank's weight during shaking. Anchoring to trim or piping would fail. Proper anchorage keeps water and gas lines intact after a quake.2022 California Plumbing Code (CPC) §507.2
A water heater is being installed in an attic above finished living space. What must be provided to catch leaks?
- a.Nothing, since the tank is listed
- b.A floor sink under the joists
- c.A drain pan piped to an approved discharge point✓
- d.Only a leak-alarm sensor
When a water heater is located where a leak would cause damage, such as an attic over living space, it must sit in a drain pan piped to an approved discharge location. The pan protects the structure below from tank or connection leaks. The drain must run to a point where the leak is visible.2022 California Plumbing Code (CPC) §507.5
A galvanized steel water heater drain pan must be at least what gauge (minimum thickness)?
- a.No. 24 gauge✓
- b.No. 30 gauge
- c.No. 16 gauge
- d.No. 28 gauge
A metallic drain pan of galvanized or aluminum steel must be at least No. 24 gauge. Plastic pans are also permitted at a minimum thickness. The pan must be corrosion resistant to hold water from a leaking tank.
A water heater drain pan must have a minimum depth of:
- a.1 inch
- b.1/2 inch
- c.3/4 inch
- d.1-1/2 inches✓
The pan must be not less than 1-1/2 inches deep so it can hold a reasonable volume before the drain carries water away. A shallower pan would overflow quickly. Depth combined with a proper drain keeps leaks contained and visible.2022 California Plumbing Code (CPC) §507.5
The drain line from a water heater pan must be at least what pipe size?
- a.2 inches
- b.1/2 inch
- c.3/4 inch✓
- d.1-1/2 inches
The pan drain must be piped with a minimum 3/4-inch pipe run by gravity to an approved discharge point. A smaller line could clog or fail to carry the leak. The drain must be independent and terminate where the discharge is readily observed.2022 California Plumbing Code (CPC) §507.5
Where should a water heater pan drain terminate?
- a.At an approved location where the discharge is readily observed✓
- b.Back into the cold water supply
- c.Into the tank's own T&P line
- d.Into a sealed, hidden cavity
The pan drain must discharge to an approved point where a leak will be readily seen, alerting the owner to a problem. It cannot combine with the T&P discharge in a way that hides either flow. Visibility is the purpose of both the pan and its drain.2022 California Plumbing Code (CPC) §507.5
A house has a water meter with a check valve installed on the service. What must be added at the water heater to control thermal expansion?
- a.A second T&P valve
- b.An expansion tank or approved expansion control device✓
- c.A larger cold water pipe
- d.A pressure-reducing valve on the hot side
When a check valve, backflow preventer, or pressure-reducing valve creates a closed system, heated water cannot expand back into the main and pressure spikes. An expansion tank or listed expansion control device must be installed to absorb that thermal expansion. Without it, the relief valve may weep or the tank may be stressed.2022 California Plumbing Code (CPC) §608.3
Thermal expansion in a domestic hot water system is primarily caused by:
- a.corrosion inside the tank
- b.water hammer from fast-closing valves
- c.water increasing in volume as it is heated✓
- d.air trapped in the piping
Water expands in volume as it is heated, and in a closed system that added volume has nowhere to go, raising system pressure. This is thermal expansion. An expansion tank absorbs the increase to protect fixtures, the tank, and the relief valve.2022 California Plumbing Code (CPC) §608.3
A gas water heater is installed in a residential garage. To reduce the risk of igniting flammable vapors, the ignition source should generally be elevated above the floor by at least:
- a.12 inches
- b.18 inches✓
- c.6 inches
- d.30 inches
Gasoline and other heavy flammable vapors tend to settle near the floor of a garage. Elevating the ignition source, such as a pilot or burner, at least 18 inches above the floor reduces the chance of ignition. Listed flammable-vapor-ignition-resistant (FVIR) heaters may change the specifics, but the 18-inch elevation is the traditional rule.
A fuel-gas water heater installed in a small closet requires combustion air primarily to:
- a.increase the water temperature
- b.supply oxygen for safe, complete combustion and proper venting✓
- c.cool the discharge pipe
- d.pressurize the expansion tank
A gas burner needs adequate combustion air so fuel burns completely and does not produce dangerous carbon monoxide. Insufficient air also causes poor draft and backdrafting of flue gases. Confined spaces must be provided with openings or ducts sized for the appliance input.
An atmospherically vented gas water heater relies on which principle to move flue gases out of the building?
- a.Positive pressure from the gas supply
- b.A powered blower on the tank
- c.The natural buoyancy of hot flue gases rising through the vent (draft)✓
- d.The T&P relief valve
A natural-draft (atmospheric) water heater vents by the buoyancy of hot combustion gases rising through a properly sized and sloped vent connector and flue. Adequate draft depends on vent height, slope, and combustion air. Blockage or poor connector slope can cause dangerous spillage of flue gases.
Under current California requirements, a new residential water closet may use a maximum flush volume of:
- a.3.5 gallons per flush
- b.2.2 gallons per flush
- c.1.28 gallons per flush✓
- d.1.6 gallons per flush
New water closets in California are limited to a maximum of 1.28 gallons per flush, a high-efficiency standard also reflected in CALGreen. Older 1.6-gpf and 3.5-gpf models are no longer compliant for new installations. The lower flush volume conserves water while still clearing the bowl.2022 California Plumbing Code (CPC) §411.2
The maximum flush volume allowed for a new urinal (other than wall-mounted) in California is generally:
- a.2.0 gallons per flush
- b.1.6 gallons per flush
- c.0.5 gallon per flush✓
- d.1.0 gallon per flush
New urinals are limited to a maximum of 0.5 gallon per flush, with high-efficiency and non-water urinals using far less. This reflects both plumbing code and CALGreen water-efficiency goals. Choosing a compliant urinal is required for new commercial restrooms.2022 California Plumbing Code (CPC) §412.2
The federal WaterSense label on a plumbing fixture indicates that the fixture:
- a.is made only of recycled brass
- b.requires no vent connection
- c.is exempt from local permits
- d.meets water-efficiency and performance criteria✓
WaterSense is an EPA program that labels fixtures meeting both water-efficiency and performance standards. A WaterSense toilet, for example, uses no more than 1.28 gpf while still flushing effectively. The label helps identify products that satisfy CALGreen efficiency goals.
A water closet must have a minimum clearance from the center of the bowl to the nearest side wall or partition of:
- a.15 inches✓
- b.10 inches
- c.12 inches
- d.21 inches
The centerline of a water closet must be at least 15 inches from any side wall or partition. This provides room to use the fixture and to service it. Adjacent fixtures require additional center-to-center spacing.2022 California Plumbing Code (CPC) §402.5
The minimum clearance required in front of a water closet, measured from the front of the bowl to any wall or fixture, is:
- a.24 inches✓
- b.15 inches
- c.12 inches
- d.18 inches
A clear space of at least 24 inches must be provided in front of a water closet or urinal. This clearance allows a person to approach and use the fixture. It is measured from the front of the fixture to the nearest obstruction.2022 California Plumbing Code (CPC) §402.5
Two water closets set side by side in a public restroom must have a minimum center-to-center spacing of:
- a.30 inches✓
- b.15 inches
- c.24 inches
- d.21 inches
Adjacent water closets must be spaced at least 30 inches center-to-center. This equals the 15-inch minimum from each centerline to a common point. Proper spacing gives each fixture room for use and cleaning.2022 California Plumbing Code (CPC) §402.5
Under CALGreen residential requirements, a lavatory (bathroom) faucet is generally limited to a maximum flow rate of about:
- a.2.2 gpm at 60 psi
- b.1.2 gpm at 60 psi✓
- c.0.35 gpm at 60 psi
- d.2.5 gpm at 80 psi
CALGreen limits residential lavatory faucets to a maximum of about 1.2 gallons per minute at 60 psi. This is stricter than older 2.2-gpm faucets. The reduced flow conserves water at hand-washing fixtures.2022 CALGreen §4.303.1
Under CALGreen, a residential showerhead is generally limited to a maximum flow rate of:
- a.0.5 gpm at 60 psi
- b.1.8 gpm at 80 psi✓
- c.2.2 gpm at 60 psi
- d.2.5 gpm at 80 psi
CALGreen limits residential showerheads to a maximum of 1.8 gallons per minute at 80 psi. Where multiple showerheads serve one shower, their combined flow generally cannot exceed the limit. This conserves both water and the energy to heat it.2022 CALGreen §4.303.1
Which statement about traps on plumbing fixtures is correct?
- a.Two fixtures may never share any drain
- b.Each plumbing fixture must be separately trapped, with limited exceptions✓
- c.A fixture needs a trap only if it drains hot water
- d.Traps are optional on floor drains
Each plumbing fixture generally must be individually trapped to keep sewer gases out of the building. Limited exceptions allow, for example, a three-compartment sink to share a trap under specific rules. The trap's water seal is the barrier against gases.2022 California Plumbing Code (CPC) §1002.1
A standard fixture trap must maintain a liquid seal of not less than 2 inches and not more than:
- a.8 inches
- b.3 inches
- c.4 inches✓
- d.6 inches
A trap seal must be between 2 and 4 inches deep unless a deep-seal trap is required by other provisions. Too shallow a seal is easily broken by siphonage; too deep can retain solids. The 2-to-4-inch range balances protection and self-cleaning.2022 California Plumbing Code (CPC) §1002.1
When setting a floor-mounted water closet, the connection to the closet flange must be made:
- a.with plumber's putty only
- b.by threading the bowl directly onto the drain
- c.watertight and gastight, typically with a wax ring or approved gasket✓
- d.using silicone caulk around the base as the only seal
The water closet must seal to the closet flange with a wax ring or listed gasket so the joint is both watertight and gastight. The bowl is then bolted down evenly to the flange. A poor seal leaks water and lets sewer gas escape at the floor.
A properly installed closet flange should sit at what position relative to the finished floor?
- a.recessed 2 inches into the subfloor
- b.at least 1 inch below the finished floor
- c.flush only when the floor is tile
- d.on top of, or flush with, the finished floor✓
The closet flange should rest on top of the finished floor so the water closet can seal correctly with the wax ring. A flange set too low leaves a gap the wax cannot bridge, causing leaks. Extension rings are used when flooring raises the floor level.