Home » 2 Reasons Why Garbage Disposal Backs Up Into Sink & How To Fix

2 Reasons Why Garbage Disposal Backs Up Into Sink & How To Fix

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.

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;

  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.

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.

How to stop disposal from backing up into the sink

Since the main reason behind this problem is clogged pipes, unclogging them is the best solution.

Possible locations of clogged pipes
Possible locations of clogged pipes

Method 1: Unclog the drain pipes using a plunger

This is the easiest way to prevent garbage disposal from backing up into the sink. By using a plunger, you can easily get rid of the clogs in the drain pipes (if they are not tough clogs, fingers crossed).

One thing to remember when using a plunger on a double sink is to block the other sinkhole using a drain strainer. Otherwise, the water you push down with the plunger will come out through the other hole with no effect on the clog. I also recommend using a half-cup plunger, not a toilet plunger. You can buy a kitchen sink plunger here (Amazon Link) if you don’t have one.

Given below is a helpful video if you have no experience plunging a kitchen sink;

Remember to run the garbage disposal after plunging. Sometimes, water will not drain until you run the garbage disposal.

If this method doesn’t work, try the next one below;

Method 2: Use a drain snake

If the plunger method doesn’t work, the next best option is a drain snake. Insert the drain snake through the sinkhole that doesn’t have a garbage disposal (you can’t pass one through the garbage disposal), and try breaking the clog.

This method can test your patience if the drain snake doesn’t end up down the drain pipes; instead of moving downwards through the T-pipe, the drain snake may move into your garbage disposal.

Here is a good drain snake (https://amzn.to/3T6n3Zb).

So probably, this method will work only if the clog is in the pipe between the garbage disposal and the second sink (See the position of Clog 2 in the picture above).

If this doesn’t work, try the next method;

Method 3: Clear the drain pipes by dismantling them

If you cannot clear the clog by plunging or drain snaking, then dismantling the drain pipes and cleaning them individually is the only option.

  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.
Unclog garbage disposal drain video

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.

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!

Frequently Asked Questions

Can I use Drano or any other chemicals to unclog the pipes?

You can use chemicals to unclog the drains, but it is the least preferred method for many reasons. One reason is, chemicals like these can damage the garbage disposal if frequently used. Another reason is, chemicals should be used only if the sink is draining slowly. If the sink is completely clogged ie, water is not draining at all, then adding chemicals won’t have any effect since they won’t reach the clogs. So when you dismantle the pipes at a later stage, you will have to deal with these chemicals.

Will clogs inside the garbage disposal cause water to back up?

If you have a double sink, and the water backs up into the other sink (the one without the disposal), then it possibly isn’t due to a clog inside the garbage disposal. If there is a clog inside the disposal, the water won’t be able to move to the other second sink.

But if the water backs up into the sink where the disposal is, and not into the other sink, then it is the disposal that is clogged, not the drain pipes. In this case, you have to unclog the garbage disposal.

Here is a detailed guide to: unclogging the garbage disposal

Further references: