How to prevent sink water from draining into my dishwasher?

Finding sink water inside your dishwasher is a nightmare.

Not only is it unhygienic and difficult to clean up after, but finding what caused it can be an even bigger problem.

So what’s causing this and how do you prevent sink water from draining into your dishwasher?

Sink water usually drains into dishwashers when there’s a clog in the pipes or some installation error. To fix this issue, find out where the clog or blockage is, whether it’s the sink line, dishwasher drain hose, air gap, or the garbage disposal. Clear the clog with either manual cleaning or an anti-clogging solution.

But is the problem caused by an installation error? And what are the proper steps to clear clogs in pipes?

Keep on reading to find out!

Why does the sink water drain into the dishwasher?

To understand why sink water is draining into your dishwasher, you must first understand the drainage system behind both. A typical sink line starts from the base where water enters through the strainer into a straight, vertical pipe. This pipe connects to a P-trap which then leads the water to the main sewage line.

A dishwasher also shares the same drainage line as the sink. The water outlet of a dishwasher, also called a drain hose, connects to the sink line which drains out into the main sewage line. This whole system is shown in the diagram below:

In some kitchens, a garbage disposal may also be installed. If there is, both the sink and dishwasher drain separately connect to it and the disposal sends water to the main sewage line.

In either case, sink water can back up into the dishwasher. So what’s causing this?

Here are a few explanations for what’s causing this problem:

1. Dishwasher Drain Hose Loop Is Too Low

A dishwasher usually sits in a kitchen’s lower shelf area. And like a washing machine, the water from a dishwasher drains from the bottom too. Since the dishwasher’s drain is located at such a low height, the water is pushed upwards through a pump into the sink line as in the diagram above.

However, if the drain hose is connected straight to the sink drain, water may travel back into the dishwasher instead of draining out to the main sewage line. So, whenever water would flow down the sink line or backup into it due to clogging, it will flow through the drain hose and down into the dishwasher with the help of gravity.

That’s why, the drain hose goes up from the bottom of the dishwasher, loops at the top, and then comes down to connect with the sink line. If the loop is placed high enough (usually to the level of the countertop), the water level can rise to the level of the sink and yet still not drain into the dishwasher.

This is because the loop naturally prevents water from flowing down through the drain hose. The diagram below explains this clearly:

So if you haven’t placed your loop high enough, simply remove the clamp or zip tie that’s holding the drain hose, and attach the loop to the highest point in the compartment, which is usually the bottom of the countertop.

2. The Sink Line Has Clogged

Many different waste materials like grease and soap can start accumulating inside the sink’s drain and cause a clog. This increases the pressure of water flowing down the drain and causes it to rise back up into the main sink line. And since the dishwasher’s drain hose is also connected to the sink line, water flows back into the dishwasher instead of the sink.

If you suspect that your sink line is clogged, you can either manually clean the pipes, use a drain snake, a plunger, or a drain opening solution. Here’s how you can do them:

  1. Manually cleaning the pipes: Manually cleaning the drainpipes allows you to thoroughly remove all the gunk that’s causing the clog. To do so, first remove the P-trap under the sink line and remove all residue with a brush. Run a drain snake through each of the pipes too, one coming from the sink and the going into the wall. Then, re-attach the P-trap and test if the water’s draining smoothly or not.
  2. Using a drain snake: Opening and cleaning the P-trap can create a lot of mess. If you want a cleaner and simpler fix, open the strainer in the sink and run a drain snake through it. Make sure to push the drain snake deep enough and twist it along to way to get all the gunk. Then, pour some hot water through the sink to flush out all the residue that you removed.
  3. Using a plunger: A plunger can remove anything clogging the pipe with just a little effort. Just place the plunger on the strainer and make sure it’s stuck tight to create an airtight seal. Then, push the plunger back and forth to free any residue that’s stuck in the pipes. You could use a toilet plunger, but considering how unhygienic that would be, you’d be better off getting a new sink plunger.
  4. Using a liquid drain cleaner: Drain cleaners are perhaps the easiest yet effective methods of clearing clogs in sink drains. All you have to do is pour the cleaner down the drain and let it sit for the recommended amount of time as per the instructions on the packaging. Drain cleaners can remove gunk or clogs quite deep inside the pipes. After it has sat, clear the drain by pouring some hot water inside it.

3. The Dishwasher Drain Has Clogged

If the sink line isn’t the issue, then chances are your dishwasher’s drainpipe has clogged. Lots of residue like oil and bits of foods get passed down the dishwasher drain hose. Over time, this residue can get stuck inside the drain hose and prevent water from draining effectively.

Luckily, cleaning a dishwasher’s drain hose is easier. Just remove the clamp holding the drain hose to the dishwasher’s pump, and the other clamp holding it to the sink line. After that, run some pressurized water through the drain hose to remove any residue stuck inside it. You could also try to seal the pipe from one side, pour some hot water inside it and let it sit for some time. The hot water will melt off any gunk stuck inside the drain hose.

4. The Air Gap Has Clogged

An air gap is a device that prevents backflow from the sink line from entering the dishwasher through the drain hose. It functions mostly like the loop we mentioned earlier, but since it further extends the height of the drain hose, it’s much more effective at stopping backflow water from entering the dishwasher.

However, an air gap can also get clogged causing dirty dishwasher water to fill the sink. As mentioned earlier, the drain hose from the dishwasher can get clogged due to the buildup of residue. So when an air gap is installed, and the dishwasher water is unable to drain into the sink line, it fills up and exits the air gap instead.

If you’re facing such a situation, simply open the head of the air gap and clean out any debris that’s stuck inside. It’s also a good idea to clean the drain hose with a drain snake or through running high-pressure water through it to allow water from the dishwasher to exit easily.

5. The Garbage Disposal Has Clogged

If you’re not careful about what you throw down your garbage disposal, it will eventually get clogged. They’ll also get clogged if you keep on feeding a lot of garbage into them without putting any water. This can clog the garbage disposal and cause water to backflow into the dishwasher hose.

Another possibility is that while installing the dishwasher drain hose to the garbage disposal, you forgot to remove the plug inside it and so water cannot drain into it. To fix this, simply unclamp the drain hose from the disposal’s inlet, remove the plug, and then refit it tightly.


Sink water backing up into the dishwasher is very unsanitary and difficult to clean up after. In most cases, this is caused by one of the problems mentioned above. All of these can be performed by yourself and are quite effective in the long run. However, if the problem is still there, you’d be better off calling a plumber to take a look.


What can you use instead of a drain cleaner to unclog a sink?

You can use a bent wire/hanger or a drain snake to manually remove the clog. Otherwise, you could use the vinegar and baking soda method to clear the blockage.

Will vinegar unclog a dishwasher drain?

A solution of vinegar and baking soda can be used to unclog a dishwasher’s drain. Simply pour the solution down the pipe, let it sit for a while, and then flush it with hot water.

Is it necessary to have air gaps installed?

In some areas, it is required by law and plumbing codes to have an air gap installed. They prevent dirty sink water from back flowing into the dishwasher.

How high should you place a dishwasher drain hose?

A dishwasher hose should typically be at least 20 inches off the ground. Otherwise, a good height is equal to the top level of the sink or the bottom of the countertop.

Why is water standing in my dishwasher?

When water is left standing in your dishwasher, it’s because it didn’t get drained properly due to a clog. These clogs happen frequently if bits and pieces of food get stuck in the drain.

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