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  • Writer's pictureRob Byrne

Dishwasher High Loop

Improper installation of dishwasher drains and traps:

One of the most common dishwasher installation defects is the "missing high loop". The purpose for this drain installation is to prevent potential airflow contamination of the dishwasher. Plumbing code states : "No domestic dishwashing machine shall be directly connected to a drainage system or food waste disposer without the proper of an approved dishwasher air gap fitting on the discharge side of the dishwashing machine."

In this application the dishwasher drain is installed with a high loop underneath the kitchen sink as shown below.

Which leads use to traps and proper installation. The main purpose of a properly installed P-trap is to allow water to be "trapped" on the bottom to prevent sewer gases from entering a home.

When it comes to installing a dishwasher high loop it must be connected "before"

P-trap. Improper installation may allow sewer gases to back up into the dishwasher.

Let's see how well you know a dishwasher.

Can you guess the only fixture that does not need a trap? i'll wait .....

give up?

If you guessed the Toilet pat yourself on the back because that is the correct answer.

The reason why is because the water in the toilet is replaced every time the toilet is used.

Running traps are another type of trap used in older homes. Running traps were located in the drainage system that are not connected directly to a fixture. These traps were designed to prevent sewer gases from entering the home.

Modern houses today use proper venting systems to eliminate the running trap.

We here at Higher Elevation Home Inspections want to make sure you and your family are ready for anything especially something like a dishwasher that can cause problems. If you have any questions feel free to give us a call anytime!

Rob Byrnes


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