In the Field · Part 4
Daily-use code: drainage slope, venting, water sizing, cleanouts, trap arms, and fixture units, with the section for each
Lesson 3 of 27~13 minFree previewCurrent as of September 2026
The exam taught the code chapter by chapter. The field uses about a dozen numbers from it every day, and an inspector checks the same dozen on every rough. This lesson is those numbers, in the order a plumber meets them on a job, each with the 2025 California Plumbing Code section that governs it: how much a drain has to fall, where cleanouts go, how long a trap arm can be, how big a drain and a vent must be for the fixtures on them, where the vent can come out of the roof, and how to size supply piping by fixture units. It is written to be read once and then kept on the phone.
What the full lesson covers
- Drainage falls 1/4 inch per foot (2 percent); 1/8 inch per foot is allowed only for 4-inch and larger building drains and only when the inspector approves it first (CPC 708.1).
- Cleanouts: at the upper end of every horizontal drain, every 100 feet, and wherever the aggregate change of direction exceeds 135 degrees; watertight and gastight (707.3, 707.4).
- Trap arms run from the trap weir to the vent: at least two pipe diameters, and no more than 30 inches for 1-1/4, 42 for 1-1/2, 60 for 2, 72 for 3, 120 for 4 inch; a water closet may be up to 6 feet from its vent (Table 1002.2).
- Size drains and vents by fixture units from Table 702.1 against Table 703.2: a 2-inch horizontal drain carries 8 DFU, a 3-inch 35, a 4-inch 216; a lavatory is 1, a tub 2, a kitchen sink 2, a washer standpipe 3, a 1.6 gpf toilet 3.
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More lessons in The Field: Method, Code, and Cases
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- 2Permits: when one is required, what is exempt, pulling it online, the inspection sequence, what inspectors look for, and handling corrections
- 3Daily-use code: drainage slope, venting, water sizing, cleanouts, trap arms, and fixture units, with the section for eachYou are here
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