Journeyman Plumber ExamDrainage, Waste, and Venting (DWV) SystemsHard
A plumber is installing a backwater valve in a building's main drain. Where should this valve typically be installed to prevent sewage from backing up into the building from the public sewer?
- AOn the highest fixture drain in the building.
- BDownstream of the building drain, just before it connects to the building sewer.
- CImmediately upstream of the building's main cleanout.
- DWithin the building's vent stack at the lowest point.
Show answer & explanationAnswer & explanation
Correct answer: B. Downstream of the building drain, just before it connects to the building sewer.
A backwater valve is designed to prevent sewage from flowing back into a building from a surcharged public sewer. Therefore, it must be installed on the building drain, downstream of all building branches, and upstream of the connection to the building sewer, typically outside the building or just inside the foundation wall.
Why the other options are wrong
- A. Installing on a fixture drain would only protect that fixture, not the entire building.
- C. While often near a cleanout, its critical placement is to protect the entire building drain from the sewer, which means downstream of the building drain.
- D. A backwater valve is a drainage device, not a vent device, and would not be installed in a vent stack.
Backwater Valve Placement
The strategic installation of a backwater valve to protect a building's entire drainage system from sewage backflow from an overloaded public sewer.
- Protects against sewer surcharging.
- Installed on the building drain.
- Must be accessible for maintenance.
- Typically at the property line or foundation egress.
Memory trick: Stop the flow, protect the home, where the sewer meets your dome!