Why Is My Dishwasher Backing Up Into My Sink?

A dishwasher backing up into a sink is one of the worst things you can see or smell in your kitchen. Well, fret not, because with a few handy tools and a dash of DIY spirit, you can tackle that drainage issue head-on. Read on to learn why your sink backs up when the dishwasher drains and how to prevent it.

Types of Dishwasher Drainage Systems

Understanding which type of dishwasher drainage system you have is crucial to troubleshooting and identifying why your sink and dishwasher are backed up. Drainage hoses can be connected via an air gap or high loop connection to your sink drain or garbage disposal. Both connections are necessary to prevent sewage from siphoning back into the dishwasher if the drain becomes clogged.

• Air Gap: A small, cylindrical or box-like device with a cap on top, typically on the countertop near the sink. It creates a physical gap between the dishwasher’s drainage hose and the sink’s drainage system, preventing potential contamination or wastewater backflow.
• High Loop: With a high loop, the drainage hose is elevated above the sink’s drain or garbage disposal unit, preventing wastewater and sewage from flowing back into the dishwasher.

Common Reasons Why Your Dishwasher Backs Up Into Sink

Many states mandate air gap connections to ensure the safe and sanitary operation of dishwashers. If you have an air gap, check it before looking at the drain for issues.

Note: Always unplug all appliances, including the dishwasher and garbage disposal, before unclogging your kitchen drain. Wear rubber gloves and be careful not to get sewage water on your skin or eyes.

Clogged Air Gap

If your air gap is clogged, the dishwasher wastewater will either leak or gush out through the air gap into your sink. Follow these steps to fix simple air gap clogs:

• Remove the air gap top cover
• Unscrew or unsnap the inner protective cap
• Remove the debris from inside the air gap if present

If you don’t see any debris, the hose connecting the air gap to the sink might be clogged. In addition, if this hose is kinked or pinched, the water flow might be obstructed, causing the water to leak at the air gap.

You can use a long bottlebrush to clear clogs from the top of the air gap. Alternatively, you can unscrew the hose clamp connection underneath, either at the waste disposal or sink drain, and clean the inside of the hose with the bottlebrush.

It may be tempting to put off cleaning your air gap in exchange for washing the dishes by hand instead. But, it’s best to get to the bottom of the issue as soon as possible. Dishwashers save water and electricity and provide superior dish sanitation.

Learn more here: Handwashing vs. Dishwasher: Which is Better?

Garbage Disposal Issues

There are two ways garbage disposals can cause water coming back up the kitchen sink from the dishwasher. Either the garbage disposal is clogged from food debris, or it’s freshly installed, and the knock pin wasn’t removed.

If your dishwasher is backing up into the garbage disposal, stuck food particles might be the issue. Before attempting to unclog the garbage disposal, ensure it’s unplugged to prevent accidental injuries. Wear gloves and avoid putting your hand into the drain, and instead, use tongs to remove debris. You might also need to detach the dishwasher hose from its inlet to clean any grime on the connection area.

For new disposals with an unremoved dishwasher plug, it’s best to contact a professional since removing the plug requires a blunt tool to avoid damaging it. In some cases, it may even be necessary to uninstall the disposal to access the plug.

Clogged Sink Drain

If your air gap and garbage disposal aren’t clogged, you may have a clog deeper in your sink drain. You can try these troubleshooting steps to unclog your sink before calling a plumber:

• Use a plunger. You can solve most sink clogs with a simple plunger. Fill your sink about halfway with water. If you have a dual-sink setup, you’ll need to block the other hole to build necessary pressure. Once ready, plunge straight up and down over the drain for 20 seconds. (Note: Avoid using chemicals when plunging. Chemicals can produce toxic fumes when applied to standing water and burn you as you plunge the sink)
• Use a plumbing snake. If your clog won’t budge under a plunger, you might be able to pull it out with a drain snake. Try unclogging from above the sink or remove the P-trap from underneath to access the drain from below. (Note: Be cautious when using the drain snake if you’ve already poured chemicals down the drain. The snake can cause the chemicals to splash around and lead to injury)
• Use a drain cleaner. Chemical cleaners can melt away many food-based clogs, but they can also damage pipes. Be extra careful when using them, and always follow brand instructions. If you decide to use chemical solutions, but fail to unclog your pipes, always let your plumber know which chemicals you applied.

Your Dishwasher May Be Backed Up

If there’s a large pool of standing water at the bottom of your dishwasher, the dishwasher itself may be clogged. In this case, there are two components you may want to clean and inspect: the dishwasher drain line and the drain filter.

To clean the drain hose, you’ll need to locate it at the back of the unit and unscrew it. Use a long bottlebrush to remove food and grease buildup and ensure it’s not kinked for optimal water flow.

To clean the drain filter — often located at the bottom of the dishwasher — you may need a screwdriver to access it. Wash the dishwasher filter according to manufacturer instructions before putting it back into place.

Want to take a less intensive approach? Pour a mix of baking soda and vinegar into the dishwasher’s bottom basket and let it sit for 15 minutes. Then, pour hot water down the basket and run the rinse cycle.

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