CSLB C-36 Plumbing ContractorRough-in PlumbingEasy
A plumber is installing a new residential drain, waste, and vent (DWV) system. A water closet (toilet) is being installed on the ground floor. What is the minimum required size for the trap arm connecting the water closet to the main horizontal drain?
- A3 inches
- B2 inches
- C1.5 inches
- D4 inches
Show answer & explanationAnswer & explanation
Correct answer: A. 3 inches
The California Plumbing Code (CPC) mandates specific pipe sizes for fixtures. A water closet (toilet) requires a minimum 3-inch trap and trap arm to ensure proper waste removal and prevent clogging.
Why the other options are wrong
- B. A 2-inch pipe is too small for a water closet trap arm and is typically used for sinks or showers.
- C. A 1.5-inch pipe is far too small for a water closet and is typically used for lavatories or small fixtures.
- D. A 4-inch pipe is larger than the minimum required for a single water closet trap arm, though it could be used for the main drain.
Water Closet Trap Arm Size
The minimum diameter of the pipe connecting a water closet's trap to the vent or drainage system, crucial for effective waste removal.
- Prevents clogs and ensures proper flushing.
- Specified by plumbing codes (e.g., CPC).
- Typically 3 inches for water closets.
Memory trick: Toilets are 'Three'; Sinks are 'Two' or 'One-and-a-Half'.