Trade Exam · Module 3
Drainage System Layout
Lay out a sanitary drainage system from the fixture to the point of disposal under the 2025 California Plumbing Code: the parts and their names, when a public sewer must be used, gravity drainage and backwater valves for low fixtures, keeping storm water out of the sanitary sewer, sizing the drain and sewer, the slope rules and their narrow exception, the fittings for each turn, and where cleanouts go.
Key Takeaways
- Flow path: fixture, trap, trap arm, branch, stack, building drain, building sewer (starting 2 ft outside the wall), public sewer or private system.
- Connect to a public sewer where one is available; it may be treated as not available if it is more than 200 ft away (713.1, 713.4).
- Storm water shall not drain into a sanitary sewer (1101.3).
- Drain by gravity where practicable (709.1). Fixtures on a floor below the next upstream manhole cover need a backwater valve (710.1).
- Size drains from total DFU with Table 703.2. The building sewer is never smaller than the building drain (717.1).
- Slope 1/4 in per ft. 1/8 in per ft only for 4 in and larger building drain (or 4 to 6 in sewer) where 1/4 is impractical and the AHJ approves (708.1, 718.1).
- Cleanouts: upper terminal of each horizontal drain, each 100 ft, each aggregate change over 135 degrees, and at the building drain to sewer junction (707.4, 719.1).
Why This Matters
The C-36 study guide from CSLB lists "piping layout and installation" in Underground and Rough Systems (22 percent of the trade exam) and "pipe sizing and venting requirements" and "shop drawings, plans, and specifications" in Planning and Estimating. Laying out a drainage system on a plan pulls those together: you trace the flow from every fixture to the point of disposal and apply the California Plumbing Code (CPC) rules at each step.
The Parts of the System, in Order
Follow the water from the fixture:
- Trap: every fixture is separately trapped (1001.2).
- Trap arm: the portion of the fixture drain between the trap and the vent (Chapter 2 definition), limited in length by Table 1002.2.
- Branch: horizontal drain collecting one or more fixture drains.
- Stack: the vertical drain line.
- Building drain: the lowest piping of the drainage system that receives the discharge from soil, waste and other drainage pipes inside the walls of the building and conveys it to the building sewer, which begins 2 feet outside the building wall (Chapter 2 definition).
- Building sewer: from the end of the building drain to a public sewer, private sewer, private sewage disposal system or other point of disposal (Chapter 2 definition).
Would you pass the C-36 today?
Take the free 21-question practice test. About 10 minutes, no account needed. You get your score by section and see exactly where you are losing points.
Take the free testKeep reading — unlock the full lesson
You're reading a free preview. Get the complete lesson plus everything you need to pass the California C-36 exam:
- All in-depth lessons, exam prep and After the License
- 1,000+ practice questions
- AI tutor (100 messages included)
- 14+ hours of audio lessons
- Full-length practice exams
- Pass guarantee
Already have an account? Sign in