CSLB C-36 Plumbing ContractorRough-in PlumbingEasy
A plumber is installing a new residential drain, waste, and vent (DWV) system. A 3-inch horizontal drain pipe receives discharge from a toilet. What is the minimum required slope for this 3-inch horizontal drain pipe, according to the California Plumbing Code (CPC)?
- A1/8 inch per foot
- B1/16 inch per foot
- C1/4 inch per foot
- D1/2 inch per foot
Show answer & explanationAnswer & explanation
Correct answer: C. 1/4 inch per foot
Proper slope is crucial for effective drainage in a DWV system. For a 3-inch horizontal drain pipe, the California Plumbing Code requires a minimum slope of 1/4 inch per foot to ensure adequate flow and prevent solids from settling.
Why the other options are wrong
- A. 1/8 inch per foot is the minimum for 4-inch or larger drains, not 3-inch.
- B. 1/16 inch per foot is insufficient for a 3-inch drain and typically not permitted for horizontal drains.
- D. 1/2 inch per foot is a steeper slope, often used to increase flow but not the minimum requirement.
Horizontal Drain Pipe Slope
The minimum downward incline required for horizontal drain pipes to ensure gravity-assisted flow of waste and prevent blockages.
- Ensures self-scouring velocity.
- Varies by pipe diameter.
- Specified in plumbing codes (e.g., CPC).
Memory trick: Drain Slope Solves Slow Sewage.