Journeyman Plumber ExamDrainage, Waste, and Venting (DWV) SystemsMedium
A plumber is installing a new branch drain line connecting to a stack. According to most plumbing codes, what is the maximum developed length of a fixture drain for a water closet (toilet) before it must connect to a vent or a vented branch?
- A4 feet (1.2 meters)
- B2 feet (0.6 meters)
- C8 feet (2.4 meters)
- D6 feet (1.8 meters)
Show answer & explanationAnswer & explanation
Correct answer: D. 6 feet (1.8 meters)
Most plumbing codes specify a maximum developed length for fixture drains to prevent trap siphonage and ensure proper venting. For water closets, this limit is typically 6 feet (1.8 meters).
Why the other options are wrong
- A. This might be acceptable for smaller fixtures but is typically insufficient for water closets.
- B. This length is generally too short for most fixture drains, especially water closets.
- C. This length is usually excessive and would likely lead to trap siphonage without proper venting.
Fixture Drain Developed Length
The maximum length of a fixture drain from its trap weir to the vent pipe connection, measured along the centerline of the pipe.
- Prevents trap siphonage.
- Varies by fixture type and pipe size.
- Ensures proper air circulation in the DWV system.
Memory trick: Long drains need a friend, or your trap will end!