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Garbage Disposal Backs Up Into Sink (Solved)

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?

The main reason the garbage disposal backs up into the sink is a clog in the drain pipe. Clogs prevent the water from moving freely, so the water takes the path of least resistance, and 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 explain in detail the root cause of this issue and how this can be solved.

Picture of water and food wastes backed up into the sink
Picture of water and food wastes backed up into the sink

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;

  1. Clogs in the drain pipes
  2. Faulty installation of the drain pipes and garbage disposal

Reason 1: 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 is 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.

You can clean the drain pipes quickly using a plunger or a drain snake. If the clog is too strong you will have to dismantle the drain pipes and clean them individually.

Reason 2: 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 remove the garbage disposal and replace it with pipe.

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, and eventually clog 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 and 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 waste properly. Regular cleaning helps the garbage disposal 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.

My name is Thomas Anderson, author of DisposalQA. I have 15 years experience working as a plumber in CA, and this is where I answer common questions about garbage disposals.