How to Install a Dishwasher Drain Hose in 6 Steps

On some dishwasher models, you can remove the screws in the front toe-kick panel and remove the cover to access the drain discharge. Still, it may be easier to pull the machine away from the wall to gain access to its backside. However you choose to do it, you’ll need to be able to reach the fitting easily.

You'll need to create a pathway following the route that your dishwasher drain hose will follow. Make the hole just above the bottom of the cabinet floor and as far back toward the wall as possible. 

Use your power drill and spade bit or hole saw to drill a hole that will accommodate the diameter of the new drain hose. A 1-1/2-inch diameter hole should be large enough. Check the top of your sink for any preexisting holes for the air gap device. You’ll use that hole later. 

If there isn’t a hole to use in your sink, you’ll need to make one. Use your power drill and an appropriate drill bit or hole saw to create a 1-3/8-inch hole in the sink deck or the countertop directly above the cabinet below.

Your dishwasher will drain through your sink plumbing. If you have a garbage disposal, it will drain into the disposal and then into the plumbing. Use a screwdriver to apply force to the inside of the dishwasher drain adapter, on the side of the disposal, to pop out the metal plug. Remove the metal plug from the inside of the disposal. Skip this step if you don’t have a garbage disposal. 

If you don’t have a garbage disposal, use your hand or large pliers to unscrew and remove one of the existing sink drain tailpieces above the P trap. Replace the tailpiece with a new sink drain tailpiece with a dishwasher drain branch. Call a local plumber for help with these steps if you get stuck.

For simplicity, we’ll start at the appliance and work our way over to the sink drain. You’ll notice that your drain hose has several diameter sizes on the ends that get progressively smaller. 

On one end of the drain hose, determine which size ring is appropriate for the discharge fitting on the dishwasher. If necessary, use your utility knife to remove parts of the drain hose end that are too large. Slip a hose clamp over the end of the hose.

Slide the hose end onto the discharge fitting on the dishwasher, and tighten the hose clamp with a screwdriver or nut driver.

Now for the easy part. Thread the drain hose's loose end through the cabinet hole. Pull enough of the hose through the hole, so there’s no slack behind the dishwasher.

Push the dishwasher back in place or replace the front access cover. Again, pull the slack out of the hose through the cabinet hole.

A siphon break can take the form of a high loop in the drain line or an air gap device. If you’re installing an air gap device, you’ll use the available hole in the sink deck or the drilled hole (from the second step). Follow one of the following procedures, depending on your setup.  

Install an Air Gap

Remove the threaded installation ring from the air gap device. From the top of the countertop or sink deck, insert the device into the designated hole. Keep in mind that the minimum height for the air gap fitting is 20 inches from the floor. 

Screw the installation ring onto the device from underneath the sink. Have a helper hold the air gap top in place as you install the ring from below if you like. 

On the loose end of the dishwasher drain hose, find the correct size ring that fits the air gap fitting and cut away the portion you don’t need with your utility knife. Slip a hose clamp over the end of the hose and slide the hose onto the small-diameter side of the air gap fitting. Tighten the clamp. 

Slide the end of the 7/8-inch air gap drain hose over the large-diameter side of the air gap fitting and tighten a hose clamp to secure it. Place another hose clamp over the other end of the hose. 

Slide the other end of the air gap hose over the new tailpiece branch fitting or the garbage disposal’s dishwasher adapter fitting and tighten the clamp

Install a High Loop

On the loose end of the dishwasher drain hose, find the diameter size ring that fits the dishwasher drain fitting on the garbage disposal or the branch on the tailpiece. Cut away the portion you don’t need with your utility knife.

Slip a hose clamp over the end of the hose and slide the hose onto the disposal’s fitting or branch fitting. The minimum height for a high loop is 20 inches from the floor. Tighten the clamp. 

Find the approximate center of the remaining drain hose, and loop several inches of pipe hanger strap around the hose. Use a screw to fasten the hanger strap and hose as high as possible in the cabinet under the sink. The idea is to elevate a portion of the hose above the P trap height.