CSLB C-36 Plumbing ContractorFixture and Appliance InstallationMedium
A plumber is installing a new dishwasher. The manufacturer's instructions specify that the dishwasher drain hose must be connected to an air gap or a high loop to prevent backflow. The client does not want an air gap installed on their countertop. What is the minimum height above the flood level rim of the sink that the high loop in the drain hose must be installed to comply with most plumbing codes?
- AAt least 12 inches above the flood level rim of the sink.
- BAs high as possible under the countertop, but not necessarily above the flood level rim.
- CBelow the flood level rim of the sink.
- DAt least 6 inches above the flood level rim of the sink.
Show answer & explanationAnswer & explanation
Correct answer: B. As high as possible under the countertop, but not necessarily above the flood level rim.
When an air gap is not used, the dishwasher drain hose must be installed with a 'high loop' to prevent backflow. This loop must be as high as possible under the countertop, ensuring it is above the flood level rim of the sink/disposer to create an effective air break.
Why the other options are wrong
- A. Similar to B, this is a specific measurement that might not be universally mandated, whereas the principle of being above the flood rim is key.
- C. Installing below the flood level rim would allow contaminated water to backflow into the dishwasher.
- D. While a high loop is needed, specific height requirements (like 6 or 12 inches) above the flood rim are less common than the general 'as high as possible' principle to ensure it's above the flood rim, which is the critical point.
Dishwasher High Loop
A method of backflow prevention for dishwasher drain lines where the flexible hose is routed significantly higher than the drain connection point, creating an air break.
- Prevents wastewater from the sink/disposer from siphoning back into the dishwasher.
- Must be installed as high as possible under the countertop.
- Acts as an alternative to an air gap device.
Memory trick: Elevate the loop to 'Eliminate Leaks' and contamination.