CSLB C-36 Plumbing ContractorRough-in PlumbingEasy
A plumbing contractor is installing a new residential drain, waste, and vent (DWV) system. What is the minimum required slope for a 4-inch horizontal drain pipe?
- A1/4 inch per foot
- B1/8 inch per foot
- C1/2 inch per foot
- D1/16 inch per foot
Show answer & explanationAnswer & explanation
Correct answer: B. 1/8 inch per foot
Proper slope ensures adequate drainage and prevents clogs. For larger diameter pipes like a 4-inch drain, a shallower slope is permissible compared to smaller pipes.
Why the other options are wrong
- A. This is the minimum required slope for drain pipes 2 1/2 inches and smaller in diameter.
- C. This slope is excessive and not typically required for horizontal drain pipes, potentially leading to premature solid deposition.
- D. This slope is generally too shallow for effective drainage in DWV systems.
Horizontal Drain Slope (3"+)
The minimum downward incline required for horizontal drain pipes 3 inches or larger in diameter to ensure proper flow and self-scouring.
- Ensures waste flows efficiently.
- Prevents solids from settling and causing clogs.
- Different slopes for different pipe diameters.
Memory trick: Slope ensures 'Waste Flows Freely' through the pipes.