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Why Is My Dishwasher Backing Up Into The Sink?

dishwasher backing up into sink and overflowing

The kitchen is the center of activity in most homes, and the sink is the heart of the kitchen. If you’re busy doing dishes, you expect everything—including the faucet, disposal, dishwasher and pipes—to work. The last thing you want is to run into any kind of problem that would result in a backed-up sink or dishwasher full of dirty, smelly water and bits of decomposing food that won’t go down. If you find your dishwasher backing up into your sink, that’s just the type of plumbing problem you’ll have on your hands, and it will need to be resolved quickly, so you can get back to your normal routine without much disruption.

There are several common causes of a dishwasher backing up into a sink, including a block in the air gap, an obstruction in your dishwasher or a clogged garbage disposal. One of the most likely culprits is a simple sink clog. Let’s take a look at each of these possibilities.

Clogged Sink

In some cases, a clog in your sink might be something minor that you can manage on your own, but be careful in how you go about it. First and foremost, consider safety. If you have a garbage disposal, make sure that you never reach into the drain to feel around for clogs without first turning off the power to the disposal. Once you do turn off the power and reach into the drain, be sure to wear plastic gloves, and proceed slowly and carefully to avoid being cut or scraped as you search for foreign articles to remove. Or, to err on the side of caution, use tongs to pull out whatever may be stuck in your sink.

Second, avoid using harsh liquid drain cleaner products. Many homeowners don’t realize these products are not good for the pipes, garbage disposal or other components related to the kitchen sink and its plumbing. Despite what the products’ manufacturers might claim on the bottle, the caustic ingredients in most drain cleaners can actually damage the pipes, disposal and other kitchen sink components, and should be avoided if possible.

Instead of using liquid drain cleaner, it’s better to try using a drain snake to unclog your sink. Depending on your level of home maintenance experience, you may be able to attempt that yourself, or you might be better off contacting a licensed plumber to diagnose and fix the problem. It’s also a good idea to prevent clogs from forming in the first place, since preventing these issues is far easier than resolving them. Avoid putting grease and fat down the drain, as these substances coat the pipes and build up over time, gradually narrowing the opening. Similarly, never put starchy items in the disposal like potatoes, rice, bread or carrots, or anything fibrous, such as asparagus or corn silk, as these can both clog pipes and also get snagged around the disposal’s moving parts.

Blockage In Dishwasher Or Garbage Disposal

Another common cause of a dishwasher backing up into the sink is an obstruction in either the dishwasher or the garbage disposal. Similar to a clogged sink, these types of problems are typically caused by excess food waste or other foreign articles that have gotten stuck and are too large, too greasy or too sticky to flush through the pipes. Sometimes it’s a relatively simple, if somewhat disgusting, matter just to reach in manually and pull out whatever it is that’s blocking the flow of water. If your garbage disposal was installed only recently, it’s also worth checking to make sure the cover on the drain plug has been removed properly.

Block In The Air Gap

Another possibility is a blocked air gap. Not all sinks have air gaps installed, but those that do have the potential of becoming blocked. Air gaps are typically installed next to the faucet for the purpose of preventing backflow. They can get clogged after longtime use, which can lead to your dishwasher being unable to drain. If you have water backing up into your sink from your dishwasher and your sink is installed with an air gap, this could be the source of the problem.

Depending on the problem you have, we’ll give you the direction you need so you can move forward with your chores. First, let’s discuss how to unclog a garbage disposal drain.

Kitchen sink with garbage disposal

How To Unclog Garbage Disposal Drain: DIY Methods And When To Call In The Pros

It’s not a good feeling when you hit the switch to run your garbage disposal and the food in the drain doesn’t go down as expected or, even worse, if your garbage disposal water comes back up. If you hear the disposal’s motor running but it’s making gurgling sounds due to water and food scraps failing to flush away, this is a good sign that your garbage disposal drain is clogged. Many homeowners wonder how to unclog garbage disposal drain: Is it a job that can be tackled by savvy homeowners, or is it one that’s better handled by a professional? And, who fixes garbage disposals? Let’s take a closer look at what it takes to unclog your garbage disposal drain.

If you have the type of system in which the dishwasher drains into the garbage disposal, as is the case with many older kitchens, food waste from the dishwasher could become clogged in the disposal and cause a backup. As with all types of kitchen sink-related clogs, prevention is easier than fixing problems after they develop. To that end, make sure to scrape as much food waste off your dishes into the trash as possible before putting them into the dishwasher, or rinse it into the disposal, as long as it’s not starchy, greasy, fibrous or otherwise unsuitable for going down the drain. Stocking the dishwasher with well-rinsed dishes makes it less likely for clogs of this type to occur.

If you have a clogged disposal, you can try removing as much waste as possible by hand and then accessing the components beneath the sink in order to manually crank it from the bottom. Always make sure to turn off the power to the disposal before doing any sort of work on your appliance, and especially before putting your hand or any other instrument into the drain. You can also first use a flashlight to peer into the drain to see whether you can spot the obstruction, before reaching in to try to dislodge it. If you have to reach in, it’s a good idea to at least wear gloves to protect your hand from cuts and scrapes, not to mention grime. Or, utilize tongs you have in your kitchen to pull out any obstructions you may see.

If the disposal seems to clog frequently, it may be that its blades are getting too dull to properly grind food waste and it’s time to consider how long garbage disposals last and whether you need to invest in a replacement. It may also be that the disposal simply isn’t the right size for your daily needs. One way to keep the blades sharper over time is to grind up a handful of ice cubes every month or so, as a part of your regular disposal maintenance routine. As part of the same routine, you can also pour in white vinegar to keep the interior parts of the disposal clean. It’s also a good idea to grind up lemon slices every few weeks to freshen the disposal.

If these methods don’t seem to help and you’re still dealing regularly with clogs, it’s a good idea to contact a licensed plumber to address the issue.

A kitchen sink and dishwasher

Can You Put Drain Cleaner In A Garbage Disposal?

It’s understandable why so many homeowners have this question. After all, when your disposal is clogged, it’s tempting to want to purchase liquid drain cleaner at the grocery store, dump it into the disposal and wait for the clog to disappear. It seems like a quick, cheap solution, right? Well, not so much when you consider the fact that using liquid drain cleaner can cause even more problems over time.

These products are made of caustic chemicals that eat away not just at the grease and other food waste that make up most clogs, but also at the pipes themselves. Their harsh chemicals can also eat away at enamel and other finishes that many people have in their kitchen sinks and pipes.

It should also come as no surprise that the chemicals in liquid drain cleaners are harsh in other ways. If you inhale fumes from these products, for example, they can irritate or even burn your eyes, lungs and nasal passages. They can do the same thing to the skin, if touched (you should never touch drain cleaner with your bare skin!), and they are extremely toxic if ingested. Many parents of young children don’t want to keep these products in the home at all, and for good reason.

Considering all these issues, plus the fact that drain cleaners are bad for the environment when they enter the water supply or the soil via residue left in bottles that are tossed into the trash, and the fact that they often aren’t even effective at loosening clogs—it just doesn’t make sense to use a drain cleaner product, no matter how inexpensive or tempting it might be. You’re better off simply contacting a plumbing professional to fix the issue through less problematic means.

A white kitchen that has a dishwasher air gap

Dishwasher Air Gap Overflow Causes

When your dishwasher is backing up into the sink, another possible cause is dishwasher air gap overflow. While not all sinks are equipped with dishwasher air gaps, those that are can become blocked after they’ve been used for a long period of time. When grease and other waste accumulates over time at some point in the line, such as at some point along the hose that runs between the drain or garbage disposal and the air gap, the dishwasher will start to back up. Rather than dirty water running out of the dishwasher, it will flow back over the dishes, making it so they aren’t perfectly cleaned or sanitized.

The air gap itself can also become blocked, as can other, connected components including the disposal. It’s also worth making sure that the air gap’s hoses aren’t kinked, preventing the free flow of water from the dishwasher. As with any DIY project, be sure to turn off the power to all components before you try investigating your sink’s air gap or working on it in any way. It might also be simpler and more time- and cost-effective simply to consult with a licensed and trained plumber who can address the issue.

Kitchen sink

What If My Sink Is Draining Into My Dishwasher?

Sometimes, when you have a clog somewhere in your kitchen sink system, the problem is that the dishwasher is draining into the sink—but other times, it’s the sink draining into dishwasher that’s causing the problem. When this happens, it’s a serious health issue, since otherwise clean dishes can become contaminated by bacteria and unsanitary waste from the sink. If you believe your sink is draining into the dishwasher, you can check all the elements previously discussed, and look for clogs in the sink itself as well as in the garbage disposal or the dishwasher’s drain line.

Again, always turn off the power to these units before starting your project, and use a flashlight, tongs and plastic gloves whenever possible. A plumber’s snake can be a useful tool when seeking to eliminate clogs from your kitchen sink system. If you can’t seem to fix this issue yourself, it’s a good idea to contact a plumber for quick, professional assistance.

ABC Can Handle Your Plumbing Issues

When something goes wrong with your kitchen sink or dishwasher, your normal routine is almost immediately impacted. Dishes can pile up quickly even as your problem gets resolved. If you’re having any issues with your plumbing or appliances that use water, contact ABC Home & Commercial Services. Our licensed professionals will be able to quickly diagnose and fix whatever has gone wrong, so you can rest assured that your pipes and appliances will be functioning correctly in short order.

Tom Riggs

Tom Riggs is the Division Manager for Mechanical Services, overseeing sales and operations for HVAC, Plumbing, Electrical, Appliance Repair, and Water Quality for all ABC Austin branches. He joined ABC in 2014 as the HVAC Operations Manager and was promoted to Mechanical Operations Manager and then Division Manager. Before ABC, he was an HVAC Service Technician, HVAC Comfort Advisor/Sales, and Operations Manager. Tom attended Universal Technical Institute. He's an avid outdoorsman and enjoys country living with his wife and two sons.

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