How to Prevent Sink Water from Draining Into My Dishwasher?

sink water dishwasher

Water, Water Everywhere Down the Sink and into the Dishwasher?

When your kitchen sink drains into your dishwasher, you’ve got a problem, not the least of which is an overflow leak from the dishwasher and/or water backing up onto the sink, which can also overflow.  Besides having to mop out, the bigger issue is you’ve got a potential health hazard. Dirty sudsy water filled with bacteria is nothing you want to leave standing in your sink or dishwasher. Dishwasher drain problems and sink water flowing into a dishwasher cannot only cause bad smells in your kitchen, more seriously it is a health hazard, so this needs to be addressed as soon as it becomes apparent.

The reason this can happen is because the water source for the sink and the dishwasher are the same—any issue with that main line can cause a backup. Sometimes a little cleaning and preventative maintenance can go a long way to avoiding this. Sometimes you’ll need to call a plumber.

Let’s look at what is causing these issues and what you can do to correct them. There are several areas to check to figure out why sink water is draining into the dishwasher. Basically, there are four potential sources of clogs that cause the  problem of sink water draining into your dishwasher:

      • Dishwasher drain hose loop or air gap leak
      • Kitchen sink drain
      • Dishwasher line
      • Garbage Disposal

Dishwasher Drain Hose

The dishwasher drain hose may not be installed correctly or it may have been accidentally pulled down to a lower center of gravity. The first thing you want to check is the drain hose loop. Locate the dishwater hookup under the sink.

Drain Hose Loop

The drain hose starts at the bottom of the dishwasher and loops up to a higher point than the kitchen sink drain, and then comes down to connect to either the kitchen sink drain, or the garbage disposal. 

The reason for the loop is so water draining from the kitchen sink won’t drain back into the dishwasher. Water follows gravity and the loop prevents backflow. Water exiting the dishwasher is driven by a pump, so it can be sent “uphill” through the dishwasher drain hose loop and into the sink or garbage disposal waste line. 

So if the loop is designed to prevent sink water draining into the dishwasher, why would it now? The drain hose is often exposed under the kitchen sink cabinet. Sometimes, particularly if it was not adequately secured during initial installation, the loop falls to below the point where it connects to the sink or disposal. Then it is only a matter of time before water from the sink finds its way into the dishwasher drain hose and flows into the bottom of your dishwasher.

Quick fix: Position the loop so it is at a high enough point above the dishwasher’s water level and secure it under the sink base cabinet so it doesn’t move again.

Drain Hose Air Gap

Some dishwasher drain hoses use an air gap to create a section of air in the dishwasher drain line hose loop to prevent dirty sink water from flowing back into the dishwasher. It usually looks like a silver cylinder set close to the rim of the kitchen sink near the faucet closest to the dishwasher. 

If your hose has an air gap and you are still getting backflow into the dishwasher, it could be damaged and you might need to replace it. It could also be that there is a clog further down the line; that clog is causing pressure that is overcoming the air gaps. In which case you need to locate the source of the clog.

Kitchen Sink Clogged Drain

A lot of food and food byproducts such as fiber and grease finds its way down kitchen sinks. Over time, drains can clog, sometimes frequently. When there is a clog in the line, water pressure in the pipes can increase and force sink water up into the dishwasher drain line.

One way to relieve the pressure is to disconnect the sink trap (P trap) underneath the sink and remove the blockage. If it is not clogged there, run a snake into the waste pipe leading into the wall behind the sink. You’ll need a bucket to catch the water and the clogged material that may come pouring out.

Another, easier way is to plunge the sink drain to break up the clogged material and force it along the waste line where it can move freely away. A word of caution, however. Using a plunger greatly increases the pressure in the line, which can defeat the air gap, even if there has been no backflow into your dishwasher. To be safe, the dishwasher drain hose should be clamped shut where it meets the sink’s drain pipes.

Dishwasher Drain Line Clog

It could be that sink water backflow into the dishwasher is not from the kitchen sink, but actually originated in the dishwasher line. This should be suspected if no other clogs seem to exist.

Food debris and grease from dishes can pass through the strainer at the bottom of the dishwasher and form sticky clumps that jam the drain line. Waste water pumped out from the dishwasher ihits the clog and then flows back into the dishwasher. 

To handle this, you have to loosen the drain hose clamps to remove the hose and run a strong stream of water through it until it is clear. 

Also check the dishwasher strainer. The strainer is in the floor of the dishwasher and is easily removable for periodic cleaning. Lift out the strainer and check beneath where it sits for any gunk that got through. You should be able to pull the gunk out with your fingers. 

This of course raises the question debated in many households as to whether or not it is better to rinse dishes before they go into the dishwasher. If you’ve experienced a clog like this one, you may think the answer is to rinse. However, this could just as easily lead to a sink drain clog from accumulated food and grease. The argument for no rinsing is that pre-rinsing is a waste of water because most modern dishwashers are well equipped to handle the dirtiest dishes.  

So which is correct/ The answer is simple and obvious. Whichever one your spouse thinks is right.

Garbage Disposal

If you have a new garbage disposal and are getting wastewater backed into the dishwasher, it may be that someone left the plug in place in the port where the dishwasher drain line is coupled to the disposal. This happens more times than you might think. We know because we’re plumbers and we see this often.

To fix this, first unplug the disposal from the electric. Remember that water and electricity don’t mix! Then remove the rubber drainage plug from the side of the disposal unit. Probe inside the port with a screwdriver for a plastic plug. If you find one, simply remove it and the draining issue could be resolved. 

If you don’t find a plug or your garbage disposal isn’t that new, it could be that waste from the dishwasher has traveled up from the drain line into the disposal and sufficiently clogged it so it now sends waste water back to the dishwasher. This can happen if the strainer has not been cleaned out routinely. It may also be that the disposal is clogged from careless operation, such as putting too much food waste into it and not properly flushing it when it is turned on.

Preventative Maintenance

There are a few things you can do to avoid clogs that could cause sink water to drain into your dishwasher. One is to scrape foodstuff off dishes before you wash them (either in the sink or the dishwasher). Pour cooking grease into a bottle that you dispose of separately and not down your plumbing. Make a regular habit of cleaning your dishwasher drain. And don’t use more dishwashing detergent that is recommended, as residue from too much detergent can build up and cause a clog.

So Why Would I Need a Plumber?

If this all seems fairly easy, and you’ve got some basic DIY skills, you should be able to clear up a clog that’s causing sink water draining into your dishwasher. Maybe. Ask yourself, though, if you really feel comfortable with tools, let alone crawling under a sink. And how handy are you, honestly. Clogged drains, incorrectly installed garbage disposals and misrouted dishwasher drain hoses can be frustrating for the DIY homeowner to resolve. 

We’ve seen more than our fair share of DIY projects gone awry that cost homeowners more than what it could have had they just called us at Benjamin Franklin Plumbing first.  We are quick, experienced, licensed, and reasonable. Our trained and experienced plumbers have seen it all: every possible way plumbing fixtures may have been wrongly installed, all kinds of corroded or missing parts most people wouldn’t think to look for and how clogs can appear in unusual places.

Benjamin Franklin Plumbing and our licensed plumbers proudly offer an on-time guarantee and a 100 percent customer satisfaction guarantee to meet all your plumbing service needs. Because we’re locally owned and operated, our plumbers are familiar with the plumbing challenges you face. If there’s any delay in providing your service, we pay!

We answer your service calls 24 hours a day at 800-259-7705, or online to request an appointment.