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Dishwasher High Loop Drain Line

Sun, 06/19/2011 - 12:45 — JoeKeresztury

Your Dishwasher High Loop Drain Line

Dishwashers work by pulling in water from the home's water supply line and then spraying and washing the dirty dishes and utensils. Then the dirty water is pumped out of the dishwasher through a drain line ordinarilly under the kitchen sink and into the home's sewer system.
It is required by most jurisdictions and manufacturers that the dishwashers drain line be installed with a high loop. This prevents the dirty water that is being drained from being inadvertently pulled back into the dishwasher or even siphoned back into the water system.
The high loop will also allow a slope, up to the high point of the drain line from the disposal. Any connection that allows the potential for waste from the disposal / disposer to enter the drain line is improper. If a garbage disposal backs up, without a high loop drain line or air gap, the waste can back up into the dishwasher and you may not be aware of it. With a properly installed high loop drain line you will become aware of the disposal backing up as it will back up into the sink in lieu of into the dishwasher.

The dishwasher high loop drain line is shown in the image. The high loop is shown properly fastened to the underside of the countertop as needed.

high loop air gap An air gap is a vent that goes up through the top of the sink or countertop. An air gap is optional, but not needed with a properly installed high loop drain line.

In the photo below (left) at a San Antonio area Home Inspection, it can be seen that there is no high loop drain line as needed. A high loop should always be installed with the dishwasher drain line to prevent backflow of waste water to the dishwasher. The high loop should be fastened, secured to the bottom of the countertop.

In the photo above (right) the dishwasher drain line was properly installed with a high loop and securely fastened to the underside of the countertop which also allows for the proper slope of the drain to the disposal.

In conclusion, high loop drain lines are an absolute neccessity with the installation of a dishwasher. If a drain line was incorrectly installed for a dishwasher, it can easily be corrected.

by Joseph W. Keresztury, your San Antonio area Home Inspector
JWK Inspections