How To Cap Off Dishwasher Drain on Garbage Disposal

How To Cap Off Dishwasher Drain on Garbage Disposal

If you’ve removed, or recently replaced your dishwasher, you may be looking for a solution to plug the hole in your garbage disposal. There is often a drainage line in place that goes from the dishwasher to the garbage disposal.

When the dishwasher is no longer installed, you essentially have a hole in your disposal. While this isn’t necessarily a major concern, it can cause problems when the garbage disposal is in use or when it gets backed up.

In order to prevent any issues from occurring, you need to cap off the dishwasher drain on your garbage disposal. This can be done simply by purchasing a plug from your local hardware store and using it to close up the hole.

It’s a very simple process and you’ll have effectively reduced the risk of any leaks from occurring underneath your sink. Let’s explore this topic in further detail and examine some other common issues that can arise from your dishwasher and garbage disposal system.

What is a Knockout Plug?

All garbage disposals will come equipped with a knockout plug that is housed inside of the unit. When your garbage disposal has one in place, you likely won’t have any leaking problems but your dishwasher may be not be draining properly.

If you’ve recently installed a new dishwasher and it’s not draining correctly, the culprit may be the knockout plug. They are, just as the name implies, designed to be knocked out. However, you only want to do this if you are connecting the disposal to a dishwasher.

However, if you do not have a dishwasher, you need to make sure that the knockout plug is still in place to prevent any leaks from occurring under the sink. If your dishwasher was recently removed, it most likely will not have the knockout plug inside the disposal anymore. In this case, you cannot replace it. Instead, you’ll have to cap it off from the outside.

Capping Off Your Garbage Disposal

Since you cannot physically replace the knockout plug in the inside of the garbage disposal, you need to plug the drainage hole. While most home improvement stores do not sell rubber caps specifically made for this, you can find similar materials that will fit the hole.

What you need to find is a rubber cap that is a 7/8” ID size and a worm drive stainless clamp. These clamps are often referred to as radiator clamps and can generally be purchased at automotive stores. This device will help to hold the rubber cap securely in place.

If you cannot find either of these, a 7/8” rubber chair leg tip can be used as an excellent alternative and is readily available in the hardware department of home improvement stores. For the clamp, you can use a plumbing clamp, also found at most home improvement stores.

While you can simply tap the cap into the hole to prevent leaks, the addition of the clamp will help hold it in place should any extensive pressure be placed on it. For example, if you ever need to use a plunger to correct a clogging problem, this will displace the plug and cause water to shoot out of the hole.

An Additional Method for Closing Off Your Dishwasher Drain Hole

If you’re removing your dishwasher and it was previously connected to your garbage disposal, you need to close off the drain hole. Follow the below steps for another method of capping off this drain. This can be done right after you’ve removed your dishwasher:

  1. Clear the area under the kitchen sink so you can easily access the garbage disposal. Put a bucket underneath where the dishwasher attaches to the drain on the disposal.
  2. Remove the dishwasher drainage hose. Do this by undoing the clamp and pulling the hose away from the barbed fitting.
  3. Place the hose into the bucket to drain.
  4. Taking a dishwasher drain connector, loosen the clamps on both sides. Push the open end of a ½ inch copper pipe cap fitting into the small side of the drain connector.
  5. Tighten the clamp to fasten the pipe cap into the connector.
  6. Slide the open end of the dishwasher connector into the barbed fitting on the drain line or disposer.
  7. Tighten the clamp to secure.
  8. Flush water through the drain to check for leaks.

How to Remove the Knockout Plug

Another common issue with the dishwasher and garbage disposal is a dishwasher that is not hooked up properly, and has drainage problems. In this instance, you likely just recently installed a new dishwasher and a small detail was overlooked.

Your dishwasher needs to be hooked up to the garbage disposal in order to drain successfully. To do this, you should remove the knockout plug from inside your garbage disposal and install the dishwasher drainage tube.

In order to remove the knockout plug, you need a hammer and a screwdriver. Locate the plug by poking into the drainage hole on your garbage disposal. If it inserts easily, the drainage plug has already been removed and the drainage problems are not caused by the knockout plug.

However, if the screwdriver hits something solid, this is the knockout plug. Use the hammer to lightly tap the back of the screwdriver around the perimeter of the plug until it falls into the disposal unit. Use your hand or pliers to reach down through the sink opening to retrieve and remove the plug.

With the knockout plug detached, you can tightly affix the drainage tubing for the dishwasher and successfully thwart your drainage issues.

Hooking Up a Dishwasher Without a Garbage Disposal

While it’s most common for your dishwasher to be hooked up to garbage disposal for drainage, what happens if you don’t have one? In this case, the dishwasher drain will be indirectly tied to the sink drain by using an air gap or it can be connected by the high-loop method, directly to the drain.

Drain Connection with Air Gap

For this method, when there is no garbage disposal, the dishwasher drain will be connected by using an air gap. An air gap fitting is a safety mechanism that is affixed on your sink or countertop, where the dishwasher hose passes on its way to the drain. It offers a pressure break in the drain line that prevents the likelihood of dirty drain water from filtering back into a dishwasher with clean dishes.

First, connect the drainage hose to the small end of the air gap. After it’s in place, use a 7/8-inch rubber hose to place the larger end of the air gap onto the skin drain’s Y-branch tailpiece. Using hose clamps, attach both ends of the drainage hose to their tailpieces. Make sure that you have no kinks in the tubing before clamping the hose in place.

Drain Connection High Loop Method

This option uses the high-loop method instead of an air gap fitting. Make sure that your local building code allows for this specific installation.

To connect the dishwasher, drain this way, you’ll need to pull as much drain hose slack as possible, loop it as high as it will go under the sink and secure in place. Using the end of the dishwasher drain line, connect it to the Y-branch tailpiece and secure it with a hose clamp.

For more common dishwasher questions, check out “How Do I Know If My Dishwasher’s Water Inlet Valve Is Bad?” and “Is It Worth Fixing a Dishwasher?

Chloe Meltzer

Real estate agent and copywriter, originally from California. Chloé brings her real estate expertise into her writing to create effective and helpful home guides for you! When not writing or selling homes, she spends her time as a digital nomad traveling the world.

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