Why Won’t My Dishwasher Drain? 

June 19th, 2022 | Around The Home, Plumbing, Toilet & Fixture

Why Won't My Dishwasher Drain?

Most people wouldn’t choose to spend their evening scrubbing dishes by hand if they had another choice. That’s why most homeowners in OC have a dishwasher to do the hard work for them. However, you may have no other choice but to pick up a sponge and some dish soap if your dishwasher isn’t draining anymore. If you want things to go back to normal as quickly as possible, you’ll want to get to the bottom of why your dishwasher isn’t draining anymore. Here is everything you need to know about how your dishwasher drains and why the process may be slowing down or stopping altogether. 

How Does Your Dishwasher Drain? 

When your dishwasher is running correctly, water comes into the dishwasher and then drains through a drain line. The drain line is either connected to your garbage disposal (if you have one) or to the sink drain. One of the most important considerations of dishwasher plumbing is to make sure dirty water doesn’t ever come back into your dishwasher to where your clean dishes are. To prevent this from happening, you’ll have one of three different systems, air gaps, high loops, or a check valve. The one that you have will depend on state and local codes. 

High Loop: Instead of using a device to prevent backflow in case of clogs, some dishwasher drains simply use gravity. A high loop is a technique of looping the dishwasher drain up to the bottom of the sink before bringing it down to connect to the garbage disposal. With the loop up above the flood line, water won’t go back the wrong way even if there’s a clog somewhere in the plumbing. It can be very effective at stopping backflow, but in California, code requires more than a simple high loop system.

Air Gap: In Tustin and the rest of OC, the code requires an air gap to pass inspection. An air gap is a small plastic device that is installed in the hole in your sink. It prevents backflow by allowing fresh air into the pipes to keep suction from drawing dirty water back into your dishwasher. 

Check Valve: A check valve is a small attachment on the drain hose that allows water through one direction, but blocks any water trying to come back the opposite way. 

Why Won’t It Drain? Common Problems and How to Fix Them

When any of these methods aren’t working correctly, your dishwasher may not drain properly anymore. Here are some of the main causes of a dishwasher that isn’t draining. 

Clogged Garbage Disposal

If you have a garbage disposal, your dishwasher will be connected to it. This allows water from your dishwasher to drain through your garbage disposal and down the drain. However, if your garbage disposal got clogged up after last night’s dinner and the problem hasn’t been resolved yet, your dishwasher won’t be able to drain anymore.

The first thing you should try when you notice your dishwasher having trouble draining is to run your garbage disposal and get it completely clear of food particles. You should also make sure to keep vegetable peelings, grease and oil, fibrous foods, hard items, and non-food items out of your disposal to keep it running properly. 

Clogged Air Gap

When your air gap becomes clogged by food or build-up, water won’t be able to flow through it anymore or it won’t be able to perform its main function. Since your air gap comes up through your sink, it’s easy to check. Unscrew the top and take a look inside to see if it’s clogged. You can clean it out with a toothbrush and some vinegar and baking soda if it looks dirty. 

Clogged Filters

If the filters inside your dishwasher are clogged up with food, it won’t be able to drain right. The type of filter you have will depend on the age of your dishwasher and the model, so make sure to check your manual for instructions on how to remove and clean the filter. Baking soda and vinegar can also help to clean the filter and remove any hard water build-up. Or you can call your OC plumber for a dishwasher repair.


If your dishwasher hasn’t been installed properly with a high loop, air gap, check valve, or some combination, you could end up with sink water coming back through into the dishwasher. If you suspect that this is the problem rather than an issue with your dishwasher, make sure to have a Tustin plumber come out for a dishwasher repair to install an air gap. You don’t want tainted water coming back into where your clean dishes are or getting into your clean water line. 

Stuck Check Valve

To work correctly, a check valve should only let water drain in one direction. Sometimes it can get stuck open or closed. Either problem can cause water to sit in your dishwasher either because it isn’t draining or because it’s coming back through. You may need a new hose or check valve. 

Clogged Disposal Hose

When your plumber is installing your air gap, the hose that goes from the air gap to the disposal (called a disposal hose) should slope down. Otherwise, you will end up with clogs in the disposal hose. You can be your own advocate and make sure it’s installed correctly. If something isn’t right, the next step is to have a plumber come and fix the slope and get rid of any clogs so that your dishwasher can drain again. 

Tips for Keeping Your Dishwasher Clog-Free

If your dishwasher has been installed correctly and everything is working as it should, the next step is maintenance. Keep grease and oil out of your plumbing, use a high-quality dish detergent that won’t cause clogs over time, and clean out your drain basket often. You can also periodically check your drain hoses for kinks or other problems. 

Has Your Dishwasher Stopped Draining? Call a Tustin Plumber!

“Why won’t my dishwasher drain?” It’s a question we get asked a lot at Moffett Plumbing & Air. But sometimes it’s not one you can answer all by yourself. If you’ve tried some of the basics like running your garbage disposal or cleaning your manual filter and water is still not draining properly, you will want to call a Tustin plumber next. Our dishwasher repair services in OC are always here for the times when a DIY fix won’t work. Give us a call for dishwasher services in your area.

Moffett Plumbing & Air is a full-service, family owned & operated plumbing & HVAC company based out of Orange, CA. Follow our blog for valuable homeowner tips, and updates from your favorite team of plumbing professionals.