Home » Blog » Why Is Garbage Disposal Backing Up Into Sink & How To Fix It

Why Is Garbage Disposal Backing Up Into Sink & How To Fix It

Garbage disposals grind up food wastes and dispose of them through the drain pipes along with plenty of water. If you have a double sink, sometimes the garbage disposal may back up into the other sink. Why does this happen?

A garbage disposal backs up into the sink due to clogs in the drain pipe. Clogs prevent the water from moving freely, so the water takes the path of least resistance, and it ends up in the other sink. This can also be due to faulty plumbing if the problem persists.

Sometimes this problem is also followed by a sewage smell coming out of the sink making the problem even worse. Let me explaini in detail what the root cause of this issue and how this can be solved.

Sink dirty from garbage disposal

Reasons for garbage disposal backing up the sink

If you have a double sink, which many houses nowadays have, you might see the water from one sink getting pushed up the other. This can happen due to;

  • Clogs in the drain pipes
  • Faulty installation of the drain pipes and garbage disposal

Clogs in the drain pipes

Clogs in the drain pipes can cause your garbage disposal to back up into the sink. As you know, clogs prevent the easy flow of water. When the garbage disposal pushes a large quantity of water into the drain pipes, most of it ends up in the other sink because that was the path of least resistance. Even though the water comes up in the other sink, both sinks will drain given enough time. But this will make the clogs even worse.

You will get plenty of warnings about this issue before it eventually causes the disposal to back up. If the water in your sink had been draining slowly, clogs were developing in the drain pipes. Cleaning the drain pipes is the only way to solve this problem.

Faulty installation of drain pipes and garbage disposal

If this problem started after installing a new garbage disposal, the villain here is faulty plumbing. Whenever you install a garbage disposal, the height of the drain pipe going into the wall should be a few inches lower than the disposal outlet’s height. But many people, when installing a new garbage disposal, do this the wrong way. As a result, they end up with a disposal outlet lower than the drainpipe outlet.

Correct and wrong way to plumb a garbage disposal

Water drains with gravity. When you mess up the drain heights, the garbage disposal and the drain pipes will always be holding water. This will lead to constant clogs in the pipes as the water and food waste don’t drain completely. So it is not surprising at all if the water and food wastes end up in the other sink.

Clearing the clogs in the pipes may solve this problem for a while, but this will happen again. Unfortunately, the only permanent solution here is to redo the plumbing or get rid of the garbage disposal.

How to fix garbage disposal backing up into sink

Since the main reason behind this problem is clogged pipes, getting rid of them is the best solution.

Possible locations of clogged pipes
Possible locations of clogged pipes

Here is how to clear clogged pipes under the kitchen sink;

  1. Unplug the garbage disposal: The garbage disposal must be unplugged to prevent any surprises.
  2. Place a bucket or basin under the pipes: Do this to prevent spillage of water.
  3. Disconnect the p-trap: The p-trap is the place that is most likely to clog. One of the main purposes of installing a p-trap is to catch any debris that is likely to clog the drain pipes further down. Once you disconnect the p-trap, clean it using a wire or bottle brush.
  4. Disconnect and clean the T-pipe connecting the disposal and the other sink: There is a T-pipe that connects the garbage disposal and the drain pipe from the other sink. This is a very likely location to find blocks. Disconnect and clean it with a bottle brush. Also, snake the drain pipes from the disposal and the other sink.
  5. Snake the drain pipe that goes into the wall: Use a plumbing snake and clean the drain pipe that goes into the wall.
  6. Reconnect all the pipes: Now all the pipes are clean, reconnect them back.
  7. Clean the garbage disposal with ice cubes: Now that the pipes are clean, the next step is to clean the garbage disposal. The best way to do this is to grind a tub of ice cubes. Add the ice cubes into the garbage disposal, turn on the water and grind them until the disposal is clear.

What clogs the drain pipes

The main and most prominent reason for clogged drain pipes is grinding wrong food wastes in the garbage disposal. Garbage disposal is not a trash can; you cannot grind everything in it. Here are some of the items that will clog the pipes when put in a garbage disposal

  • Oils, grease, and fat: Pouring any of these into the garbage disposal will clog the drain pipes for sure. These materials will solidify in the drain pipes catching all the food debris going through, eventually clogging the pipes.
  • Fibrous vegetables: Corn husks and vegetables like celery contain fibers that will accumulate and form a net in the drain pipes, eventually preventing water from draining.
  • Coffee grounds, eggshells: These items will sediment in the drainpipes adding further load to the drainage system.
  • Rice, pasta, potato peels, etc.: These are starchy food items that form a sticky paste once ground and wet. Imagine what happens when they end up in the drain pipes.

Clogs can also happen if your garbage disposal is too old and cannot grind the food wastes properly. Regular cleaning helps the garbage disposals blades to stay sharp and grind well. If the grinding is not good even though you maintain it properly, it is time to buy a new garbage disposal.

Getting rid of the garbage disposal

The second reason for garbage disposal backing up is the faulty installation of the garbage disposal. This mostly happens when you newly installed a garbage disposal on an old plumbing system. The sinks in old houses tend to have the drainpipe outlet much higher than in new houses. So when you remodel the kitchen by installing a garbage disposal or a deep sink, it affects the drainage system as these new installations require a drain outlet lower to the wall.

If this is the problem, it is better to call a plumber to find a solution. You will possibly have to open the wall and lower the drain pipes or get rid of the garbage disposal or the deep sink. If it is a professional plumber who did the new installations, hire a different one!

Further references:

My name is Thomas Anderson, and I have worked briefly as a plumber. Even though I am currently working on a different career path I still help out my friends and family with their plumbing issues. This is a hobby blog where I share my knowledge with the audience through random articles. Through this blog, I hope to address some common questions about garbage disposals.