As part of the overall installation of a dishwasher, hooking up the drain is usually pretty easy, but it's important to understand the different methods of options when connecting a dishwasher drain, with or without a garbage disposal.
If you are removing a dishwasher and replacing it with a new one, it is usually easiest to simply copy the same drain hookups that were used on the old dishwasher. But if you are adding a dishwasher for the first time, then you may need to install a special drain fitting to give the dishwasher a place to drain. The different drain variations you may encounter include:
- Drain line connected through an air gap to garbage disposer
- Drain line connected through an air gap directly to the drain
- Drain line configured in a "high loop" to garbage disposer
- Drain line configured in a "high loop" directly to drain
An air gap fitting is a safety device mounted on your sink or countertop, through which the dishwasher hose passes on its way to the drain. It provides a pressure break in the drain line that prevents the possibility of dirty drain water being back-siphoned into a dishwasher filled with clean dishes, thereby contaminating them. Not all dishwashers use this device; another alternative is what is known as the "high loop" installation, in which the drain line loops up under the sink base cabinet to a point above the dishwasher's water level.
The tools and materials you need to connect a dishwasher drain will vary, depending on the configuration and whether or not there is an air gap.
Equipment / Tools
- Utility knife
- 7/8-inch (inside diameter) drain hose
- Hose clamps
- Y-branch drain tailpiece (if needed)
- Garbage disposal drain adapter (if needed)
Drain Connection With Air Gap and Garbage Disposal
If an air gap fitting is used, there will be two lengths of drain hose: the factory drain hose on the dishwasher, which runs from the dishwasher to the smaller of the two tailpieces on the air gap, and a 7/8-inch (inside diameter) hose that runs from the other tailpiece on the air gap to the dishwasher nipple on the garbage disposal.
Connect Hose to Air Gap
Cut down the dishwasher drain hose from the dishwasher so it is just long enough to reach the smaller tailpiece on the air gap fitting mounted on the countertop or sink deck. Connect the end of this hose to the air gap, using a hose clamp.
Connect Hose to Garbage Disposal
The large end of the air gap is then connected down to the garbage disposal with a 7/8-inch rubber hose. Connect both ends of the hose with hose clamps (one on the air gap and one on the garbage disposal inlet nipple).
Make sure you do not have any kinks in the 7/8-inch hose when making the connections because this will restrict the flow of drain water and may cause a blockage over time. If it is too long, this hose may need to be trimmed down to size to prevent kinking.
Drain Connection With Air Gap (But No Garbage Disposal)
When connecting a dishwasher drain with an air gap, but where there is no garbage disposal, the drain hose is indirectly tied to the sink drain through the air gap
Connect Hose to Air Gap
First, connect the dishwasher drain hose onto the small side of the air gap, mounted on the countertop or sink deck. You may need to use some force to slide the hose onto the air gap fitting.
Connect Hose to Drain Pipe
Then, hook up the larger side of the air gap to the Y-branch tailpiece on the sink drain, using a 7/8-inch rubber hose. Y-branch tailpieces are available in two sizes, so make sure to get the size that fits the 7/8-inch hose running from the air gap.
Secure With Hose Clamps
Connect both ends of the hose to their tailpieces by using hose clamps. Before you clamp the hose in place, make sure there are no kinks in the tubing. Hoses that are too long can be trimmed down to size.
Drain Connection Using High Loop to Garbage Disposal
Before installing this type of dishwasher drain connection, make sure that the local building codes allow for the high loop method instead of an air gap. In some communities, the high-loop method may not be allowed.
Prepare the Drain Hose
Pull as much of the drain hose as possible from behind the dishwasher. You will need this extra drain hose to create the high loop before connecting the dishwasher hose into the garbage disposal.
Loop the Drain Hose
Pull the dishwasher drain hose up and strap it in place as high up as possible under the sink. This high loop will help prevent wastewater from siphoning back into the dishwasher from the garbage disposal. A large pipe clamp or piece of flexible pipe strapping can be used to secure the hose to the underside of the countertop or to the wall near the countertop.
Connect the Hose
Connect the dishwasher drain tube directly into the garbage disposer with hose clamps. You may need a dishwasher connector fitting to make the transition from the hose to the garbage disposal. One end of the connector attaches to the smaller drain hose, and the other end has a larger 7/8-inch fitting that attaches to the garbage disposal.
Drain Connection Using High Loop Directly to Drain
Once again, check the local building codes to make sure that the high loop method is legal in your area.
Loop the Drain Hose
Pull as much of the drain line as possible from behind the dishwasher and loop it as high as possible under the sink and strap it in place. This will prevent wastewater from the sink drain from siphoning back into the dishwasher.
Attach Hose to Sink Drain
Take the end of the dishwasher drain line and attach it to the Y-branch tailpiece, securing it with a hose clamp. Y-branch tailpieces can be purchased that match the size of your dishwasher drain hose.