CSLB C-36 Plumbing ContractorFixture and Appliance InstallationMedium
A plumber is installing a washing machine in a laundry room. The manufacturer's instructions state that the washing machine drain hose must be inserted into a standpipe. What is the primary purpose of this standpipe arrangement?
- ATo collect lint and debris before it enters the main drainage system.
- BTo create an air gap that prevents wastewater from being siphoned back into the washing machine.
- CTo ensure that the drain hose maintains a constant downward slope for gravity drainage.
- DTo prevent the washing machine from vibrating excessively during the spin cycle.
Show answer & explanationAnswer & explanation
Correct answer: B. To create an air gap that prevents wastewater from being siphoned back into the washing machine.
The standpipe, in conjunction with the drain hose inserted into it, effectively creates an air gap. This air gap is crucial for preventing back-siphonage, where dirty wastewater from the drain system could be drawn back into the washing machine, contaminating clothes or the water supply.
Why the other options are wrong
- A. Some standpipes might have lint traps, but the primary code-driven purpose of the standpipe itself is backflow prevention via an air gap.
- C. While a downward slope is important for drainage, the standpipe's primary role is specific to preventing backflow, not just ensuring slope.
- D. While proper installation can reduce vibration, the standpipe itself is not primarily for vibration dampening.
Washing Machine Standpipe Purpose
A vertical pipe into which a washing machine's drain hose is inserted, primarily to create an air gap for backflow prevention.
- Prevents back-siphonage of dirty water into the washing machine.
- Creates an air gap between the drain hose and the drainage system.
- Required by plumbing codes for health and safety.
Memory trick: Standpipe tall, prevents the fall of dirty water, saves us all.