Journeyman Plumber ExamDrainage, Waste, and Venting (DWV) SystemsMedium
A plumber is installing a new residential DWV system. The main building drain connects to the public sewer at the property line. What is the minimum size, in inches, required for a cleanout installed at the junction of the building drain and the building sewer?
- A4 inches
- B2 inches
- C6 inches
- D3 inches
Show answer & explanationAnswer & explanation
Correct answer: A. 4 inches
According to most plumbing codes, a cleanout at the junction of the building drain and building sewer must be at least as large as the pipe it serves, but not less than 4 inches in diameter.
Why the other options are wrong
- B. This size is typically too small for a main building drain/sewer cleanout.
- C. While a 6-inch cleanout would be acceptable, it is not the minimum required size for this specific location if the pipe is smaller.
- D. While a 3-inch drain might exist, the cleanout at this critical junction must be larger.
Building Drain/Sewer Cleanout Size
The minimum diameter required for a cleanout located at the critical junction between a building's internal drainage system and the external sewer connection.
- Must be at least the size of the pipe served.
- Minimum 4 inches at building drain/sewer junction.
- Ensures adequate access for clearing blockages.
Memory trick: Main drain, main access, four inches or more.