CSLB C-36 Plumbing ContractorRough-in PlumbingEasy
A plumbing contractor is installing a new residential drain, waste, and vent (DWV) system. For a 4-inch horizontal drain pipe, what is the minimum required slope per foot to ensure proper drainage?
- A1/8 inch per foot
- B1/2 inch per foot
- C1/16 inch per foot
- D1/4 inch per foot
Show answer & explanationAnswer & explanation
Correct answer: D. 1/4 inch per foot
The California Plumbing Code (CPC) specifies minimum slopes for horizontal drainage piping. For pipes 2-1/2 inches or larger, the minimum slope is 1/4 inch per foot.
Why the other options are wrong
- A. This slope is standard for smaller diameter pipes (2 inches or less), but not for 4-inch pipes.
- B. While this slope would drain, it is more than the minimum required and could lead to faster liquid flow leaving solids behind.
- C. This slope is generally too shallow for effective drainage and can lead to clogs.
Drain Pipe Slope
The necessary downward incline of horizontal drainage piping to ensure wastewater flows properly by gravity and solids are carried away.
- Ensures proper drainage and prevents clogs.
- Varies based on pipe diameter.
- Measured in inches per foot.
Memory trick: Drainage Slopes: Small pipes need less, big pipes need more push.