A plumber is installing a new clothes washing machine. The manufacturer's instructions state that the hot and cold water supply lines must be connected to a washing machine outlet box that includes integral shut-off valves and a standpipe for the drain. What is the primary reason for requiring a standpipe for the washing machine drain?
- ATo create an air gap and prevent backflow of wastewater into the potable water supply.
- BTo prevent the washing machine from vibrating excessively during operation.
- CTo allow for easy access to clean out lint and debris from the drain line.
- DTo ensure the washing machine always drains completely after each cycle.
Show answer & explanationAnswer & explanation
Correct answer: A. To create an air gap and prevent backflow of wastewater into the potable water supply.
A standpipe provides the necessary height for the washing machine's drain hose to terminate into, ensuring an air gap between the end of the drain hose and the flood level rim of the standpipe. This air gap is a critical backflow prevention measure, preventing potentially contaminated wastewater from being siphoned back into the potable water system.
Why the other options are wrong
- B. Vibration is managed by leveling the machine and ensuring stable footing, not the standpipe.
- C. While some access for cleaning is a benefit, the primary reason for a standpipe is backflow prevention, not cleanout access.
- D. The washing machine's pump ensures it drains completely; the standpipe's function is unrelated to complete drainage.
Washing Machine Standpipe Purpose
The primary purpose of a washing machine standpipe is to provide an indirect waste connection through an air gap, preventing back-siphonage of contaminated laundry wastewater into the potable water supply system.
- Creates an air gap.
- Prevents backflow/back-siphonage.
- Protects potable water supply.
Memory trick: Standpipe's height keeps dirty water out of sight (and out of your drinking water).