Dishwasher High Loop – Common Inspection Defects

The Dishwasher High Loop

Example of a poorly installed dishwasher high loop.Poor dishwasher drain line configuration is a common defect found during an inspection.  Thankfully, fixing the dishwasher high loop is typically an easy fix that you can correct in matter of minutes.  If you have no earthly idea what the dishwasher high loop is, or why it’s important, your in the right place.  Before we get into how to correct the line, were going to talk about what the purpose of the high loop is and why it’s important to have one.

So What is A Dishwasher High Loop?

Diagram of a dishwasher high loop.A high loop is the point in the dishwasher drain line where it elevates just prior to connecting to the sink plumbing.  The drain line should be positioned high in the cabinet and secured as close as possible to the countertop to provide the best function.  The line is then connected to the sink tailpipe prior to the p-trap.  Some garbage disposals have a connection for the dishwasher, however given the option, it is recommended to utilize a tailpipe.  The disposal can act as a pump and force waste water back through the pipe into the dishwasher.

Why is A High Loop Important?

Exampleof waste water backingup from disposal to dishwasher.Simply put, a high loop in the drain line is the easiest way to prevent wastewater from re-entering the dishwasher.  Imagine a time your kitchen sink got clogged.  Do you remember the foul water that filled the sink?  Without that high loop, gravity takes over and that water flows back down the dishwasher drain line and can cause contaminated water to pool in the bottom of your dishwasher.  So much for clean dishes….

The Dishwasher High Loop vs an Air Gap

Disgram of a dishwasher air gap.An airgap is a device that replaces the high loop and is mounted at the sink.  An air gap is the only true way to prevent all possible back siphoning but is not required by all jurisdictions.  The device is mounted to the sink and allows air to enter dishwasher drain line in the event of a vacuum and siphoning.  This prevents wastewater from being sucked through the line from the sink plumbing.  If you notice consistent issues with water pooling in your dishwasher or siphoning, you may wish to have an air gap installed.  In most dishwasher installations however, a high loop works well.

Installing A High Loop

So now the all-important question, how do I install the dishwasher high loop?  Well, there is no single way, and your situation and setup will vary.  One of the simplest and most effective ways I have seen is using a screw-eye and a zip-tie. Just remember the key is to have it as high as possible, and make sure it does not get in the way of other plumbing components just as the sprayer wand hose which moves within the cabinet.

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