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high loop

A high loop is where the dishwasher drain hose is elevated as high as possible underneath the kitchen sink in order to prevent dirty water in the sink or garbage disposal from being sucked or siphoned back into the dishwasher and possibly contaminating your clean dishes.

If you are not sure what a dishwasher drain hose looks like, the photo below shows a typical dishwasher drain hose.

typical dishwasher drain hose

A dishwasher high loop accomplishes this by keeping some air in the upper part of the drain line. This air should then be able to break the siphon if dirty water begins to flow backward (siphon) from your sink or disposal toward the dishwasher through the dishwasher drain hose.

The lack of a high loop on a dishwasher drain is one of the most common defects that we write up as a deficiency during home inspections. Fortunately, it’s also one of the simplest defects to correct. It should only take you about five minutes, and should certainly cost less than five dollars (it’ll probably cost nothing) to fix a missing high loop.

How to Install a Dishwasher High Loop

All you have to do to make a high loop is raise a section of the dishwasher drain hose as high as you can underneath the kitchen sink and secure it in place to form a loop.

The drain hose can be held in place underneath the kitchen sink by using a metal bracket, plumber’s tape, a zip tie, a piece of wire, etc. Just put one of these items around the drain hose and hold it in place with a nail or screw in the upper part of the cabinet. That’s all there is to it. 

See the photo at the top of this post to see basically what you need to do to create a high loop. In that photo, the drain hose has been held in place to form the high loop with a piece of wire.

Below is a drawing showing basically what a dishwasher high loop will look like.

dishwasher high loop
Amazon even sells a high loop bracket that also appears to be very simple to install (see photo below).
high loop bracket

If Your Dishwasher Has a Built-In High Loop, Do You Still Need to Install Another One?

The short answer is yes. Code requires a high loop under the sink even if your dishwasher has one built-in. Most code inspectors will require a high loop under your sink before they will sign off on the installation.

Where to Install a Dishwasher Drain Line

First, it is important that the dishwasher drain line be installed between the sink drain and the P-trap. It should never be installed after the P-trap because this would allow sewer gases in the sewer line to enter the home through the dishwasher via the dishwasher drain line.

The ideal place to install the dishwasher drain line is on the drainpipe just under the kitchen sink as shown in the photos below.

drain pipe
drain pipe

Many dishwasher drain lines are installed at the garbage disposal. While this is allowed, it is not the best method to use. The reason for this is that the disposal or the drain line after the disposal can become clogged.

Since the garbage disposal acts like a pump, the water in the disposal can be pumped over to the other side of the sink, if you have a double sink. The disposal can also pump this nasty, dirty water back into the dishwasher through the drain line. That’s why you should avoid attaching the drain line to the disposal. (Below are two photos of dishwasher drain lines attached to the garbage disposal.)

dishwasher drain line
dishwasher drain line

What is an Air Gap?

delta dishwasher air gapsA dishwasher air gap is a device that is designed to prevent contaminated water from the sink or garbage disposal from flowing back to the dishwasher due to backflow through the dishwasher drain line.

The air gap is mounted just above the kitchen sink on the countertop.  (The photo to the right shows the part of an air gap that is visible on the countertop.)

An air gap is a simple, low-cost device that helps to prevent the clean dishes in your dishwasher from being contaminated by dirty water that flows back into your dishwasher if, for example, your garbage disposal gets clogged and causes dirty water to flow backward through the drain line into your dishwasher.

This backflow of dirty water is caused by a phenomenon called a cross-connection. (See our other blog for a discussion of cross-connections.) Air gaps are designed to prevent a cross connection at the dishwasher. The air gap keeps the hose that carries dirty water from the dishwasher separate from the hose that takes the dirty water to the drain underneath the sink. Since the two hoses are completely separate, the danger of wastewater flowing back into your clean dishwasher is eliminated.


Again, a dishwasher high loop is commonly overlooked, but it is important and very simple to install. Take a look under your kitchen sink and see if you already have one. Odds are, you don’t. If the odds are correct, take about five minutes and install one. That’ll be one less thing you have to worry about.

© 2022 Mike Morgan

This article was written by Mike Morgan, the owner of Morgan Inspection Services. Morgan Inspection Services has been providing home, septic and well inspection services throughout the central Texas area since 2002. He can be reached at 325-998-4663 or at No article, or portion thereof, may be reproduced or copied without prior written consent of Mike Morgan.

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