CSLB Trade — Plumbing (C-36) Practice Test
Practice stays free. The full CSLB Class C-36 — Plumbing (Trade Exam) study guide is the material itself, taught start to finish — a downloadable PDF + EPUB you keep.
| Administering body | Contractors State License Board (CSLB), California Department of Consumer Affairs — exam delivered by PSI Services LLC |
|---|---|
| Questions | Not published by CSLB What we read and found nothing in: CSLB — Step 7: Studying for the Examination |
| Time limit | 210 minutes |
| Passing score | Not published by CSLB What we read and found nothing in: CSLB — Step 7: Studying for the Examination |
| Fees |
Source: CSLB — List of All CSLB Fees |
| Languages offered | English · Spanish |
Frequently asked questions
How many CSLB C-36 Plumbing trade questions are here?+
360+ original practice questions across the content areas of the C-36 plumbing exam — Planning & Estimating, Water Supply & Distribution, Drainage/Waste/Vent, Fixtures & Water Heaters, Gas Piping, and Safety — with California Plumbing Code (UPC-based) references.
Is the C-36 trade exam separate from the Law & Business exam?+
Yes. To get a C-36 Plumbing contractor license you must pass BOTH the Law & Business exam AND this C-36 trade exam. They are two separate exams, each about 3.5 hours at a PSI testing center.
Which code is the C-36 exam based on?+
The California Plumbing Code (Title 24, Part 5), which is based on the Uniform Plumbing Code (UPC). Expect code-lookup, pipe sizing by fixture units, drainage slope and venting, backflow/cross-connection, water heaters, and gas piping. A calculator is provided.
Are these the real CSLB exam questions?+
No. Every question is 100% original, written from public sources (the California Plumbing Code / UPC and Cal/OSHA Title 8). We never copy real exam questions or paid prep material.
Can I study the C-36 material in Chinese or Spanish?+
Yes — PrepPass practice and study guides are in English, 中文 and Español. The official CSLB exam is offered in English (Spanish and translator accommodations may be available through CSLB); you can switch the question language to English any time to rehearse the wording you'll see at the test center.
Sample practice questions
A few real questions from this free bank, with full explanations. Use the practice tool above for the whole set.
- 1. Water Supply & Distribution
A single-family dwelling has a total demand of 22 water supply fixture units (WSFU). Using the code sizing tables, which is the smallest nominal water service pipe size that is generally acceptable for a building water service?
- a.1/4 inch
- b.3/4 inch
- c.3/8 inch
- d.1/2 inch
Answer: b
Explanation: The code establishes 3/4 inch as the minimum nominal size for a building water service serving a typical dwelling, and 22 WSFU falls within its capacity for normal developed lengths and pressure. A 1/2 inch, 3/8 inch, or 1/4 inch service is below the allowed minimum for a building supply and would not be code-compliant.
Source: 2022 California Plumbing Code (CPC) §610.0
- 2. Water Supply & Distribution
What is the essential difference between back-siphonage and backpressure backflow?
- a.They are identical
- b.Back-siphonage is caused by negative (sub-atmospheric) pressure in the supply, while backpressure is caused by downstream pressure exceeding supply pressure
- c.Backpressure only occurs in drainage systems
- d.Back-siphonage requires a pump; backpressure never does
Answer: b
Explanation: Back-siphonage results from negative pressure (a partial vacuum) in the supply pulling water backward, while backpressure occurs when downstream pressure exceeds the supply and pushes water backward. They are not identical, back-siphonage does not require a pump, and backpressure occurs in pressurized water systems, not just drainage.
Source: 2022 California Plumbing Code (CPC) §603.0
- 3. Drainage, Waste & Vent
A vent terminal near an openable window or door must terminate at least:
- a.3 feet above or 10 feet horizontally away from the opening
- b.2 feet above or 6 feet away
- c.5 feet above or 15 feet away
- d.1 foot above or 5 feet away
Answer: a
Explanation: A vent must terminate at least 3 feet above or at least 10 feet horizontally from any openable window, door, or air intake within 10 feet, to keep sewer gas out of the building. The other combinations are less than the code-required separation and could allow gas to re-enter.
Source: 2022 California Plumbing Code (CPC) §906.2
- 4. Drainage, Waste & Vent
Loss of a trap seal from siphonage or back pressure is primarily prevented by:
- a.Proper venting of the drainage system
- b.Adding a cleanout
- c.Using a larger trap
- d.A deeper seal alone
Answer: a
Explanation: Venting introduces air to equalize pressure in the drainage system, which prevents siphonage and back pressure from pulling or pushing out the trap seal. A larger trap or a deeper seal alone does not correct the pressure imbalance, and a cleanout serves maintenance, not seal protection.
Source: 2022 California Plumbing Code (CPC) §901.0
- 5. Drainage, Waste & Vent
The size of a hydromechanical grease interceptor is primarily selected based on…
- a.the color of the discharge
- b.the number of restrooms in the building
- c.the length of the drain line only
- d.the flow rate (GPM) of the fixtures it serves and its rated grease retention capacity
Answer: d
Explanation: A hydromechanical (point-of-use) grease interceptor is selected by the flow rate in GPM it must handle and its rated grease capacity in pounds. A flow-control fitting limits flow to the rated GPM so grease can separate. Undersizing lets grease pass straight through to the sewer.
Source: 2022 California Plumbing Code (CPC) §1014.0
- 6. Fixtures & Water Heaters
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
Answer: d
Explanation: 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.
Source: 2022 California Plumbing Code (CPC) §507.5
- 7. Fixtures & Water Heaters
The temperature-sensing element of a water heater T&P relief valve must be located so that it senses:
- a.the incoming cold water
- b.the water in the top 6 inches of the tank
- c.the flue gas temperature
- d.the room air temperature
Answer: b
Explanation: The T&P valve's temperature element must extend into the top 6 inches of the tank, where the water is hottest, so it responds to dangerous overheating. Sensing cooler water lower in the tank would delay relief. Correct placement is essential to the valve's protective function.
Source: 2022 California Plumbing Code (CPC) §608.3
- 8. Gas Piping
Why must clearances to combustibles for a single-wall metal vent connector and for Type B vent be respected during installation?
- a.Because vent surfaces can reach temperatures that ignite nearby wood or paper if the listed clearance is not maintained
- b.Because vents never get hot
- c.Clearances apply only to gas piping, not vents
- d.Only to make the job look neat
Answer: a
Explanation: A vent connector carries hot combustion products, and its surface can reach temperatures that ignite adjacent combustibles if the listed clearance is not kept. Single-wall connectors require larger clearances than double-wall Type B vent because they radiate more heat. Always follow the clearance-to-combustibles values on the vent listing and appliance instructions.
- 9. Planning & Estimating
What is the main purpose of a plumbing fixture schedule on a set of plans?
- a.To list the paint finishes
- b.To give the electrical load calculations
- c.To show soil-bearing capacity
- d.To identify each fixture type, its connection sizes, and its mark so it can be matched to the floor plan
Answer: d
Explanation: 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.
- 10. Safety
A trench that was safe yesterday saw heavy overnight rain. How often does Cal/OSHA require a competent person to inspect an excavation where workers will be exposed?
- a.Daily before each shift, and after any rain or condition that increases hazards
- b.Only once, before the first entry of the project
- c.Only when the customer requests it
- d.Weekly
Answer: a
Explanation: Title 8 §1541 requires the competent person to inspect excavations, adjacent areas, and protective systems daily before work starts, as needed throughout the shift, and after any event that increases hazards such as rainstorms. Water saturates soil, adds weight, and dramatically raises cave-in risk. If hazards are found, workers must be removed until corrections are made.
Source: Cal/OSHA Title 8 §1541
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