Special Considerations for Dishwasher Drain Connections

  • 01 of 05

    Introduction

    Close up of dishwasher with door open in British home.
    Nick Callaghan / Getty Images

    As part of the overall installation of a dishwasher, hooking up the drain is usually pretty easy, but there are a few things to consider before you do it. Take a look at the different methods of connecting a dishwasher drain, so you will know your options when installing a garbage disposal or a new dishwasher.

    If you are replacing an existing one, it is usually easier to simply copy the same drain hookups that were used on the old dishwasher.  If you are adding a dishwasher for the first time,...MORE then you will need to install a special drain fitting to give the dishwasher a place to drain.

    The following pages will show several different variations you may encounter, including:

    • Drain line connected through an air gap to garbage disposer.
    • Drain line connected through an air gap directly to drain.
    • Drain line configured in a "high loop" to garbage disposer.
    • Drain line configured in a "high loop" directly to drain.

    TIP: 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-syphoned 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 above the water level below the sink base cabinet. 

    Continue to 2 of 5 below.
  • 02 of 05

    Air Gap to Garbage Disposal

    If an air gap fitting is used, the dishwasher drain hose has a large end on it that will have to be trimmed to fit into the small end of the air gap. Connect the trimmed dishwasher drain into the small side of the air gap with a hose clamp.

    The large end of the air gap is then connected down to the garbage disposal with a 7/8” rubber hose. Connect both ends of the hose with hose clamps (one on the air gap and one on the garbage disposal inlet pipe). Make sure you do not have any kinks in the 7/8”...MORE tube when making the connections because this will restrict draining and may cause a blockage over time. Twist the tubing so it is as round and fully open as possible before trimming the hose to size.

    Continue to 3 of 5 below.
  • 03 of 05

    Air Gap to the Drain (No Garbage Disposal)

    When connecting a dishwasher drain with an air gap without a garbage disposal, the dishwasher air gap connection is indirectly tied to the sink drain.

    First, the dishwasher drain hose will connect onto the small side of the air gap, using a  hose clamp.

    The larger side of the air gap will be hooked up to the Y-branch tailpiece on the sink drain with a 7/8" rubber hose. Y-branch tailpieces are available in two sizes, so make sure to get the size that fits 7/8" tubing running from the air...MORE gap. Connect both ends of the hose by using hose clamps. Before you clamp the hose in place, make sure there are no kinks in the tubing.

    Continue to 4 of 5 below.
  • 04 of 05

    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 air gap may be mandatory. 

    Pull as much of the drain hose as possible from behind the dishwasher. You will use the extra drain hose to create the high loop before connecting the dishwasher drain into the garbage disposal. Pull the dishwasher drain hose up and strap it in place as high up as possible under the sink. This...MORE high loop will help prevent waste water from siphoning back into the dishwasher from the garbage disposal.

    Connect the dishwasher drain tube directly into the garbage disposer with hose clamps. If all you have is a small end on the dishwasher drain, then you can get a dishwasher connector. One end of the connector will attach onto the small drain tubing, and the other end will have a larger 7/8” end that will hook into the garbage disposal.

    Continue to 5 of 5 below.
  • 05 of 05

    High Loop Directly to Drain

    Once again, be sure to check the local building codes to make sure that the high loop method is legal in your area. 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 waste water from the sink drain from siphoning back into the dishwasher.

    Take the end of the dishwasher drain line and attach it to the Y-branch tailpiece and connect it with a hose clamp. Y-branch tailpieces can be purchased...MORE that match the size of your dishwasher drain hose.