Many homeowners complain their sink only drains when garbage disposal is on. 

If you are having a similar problem, don’t panic. And you don’t necessarily have to call a plumber. 

This is an everyday culinary issue. And 9 out of 10 times, it is due to too much garbage and filth stock in drain pipes needing more flushing water. 

That is why it ONLY drains when you try to fee it with the garbage disposal. 

So if the kitchen sink won’t drain unless garbage disposal is running, take a breath of relief because the article addresses this issue in a minute. 

How Does A Garbage Disposal Work? 

First of all, the garbage disposal is mounted underneath the sink. Once flipped on, the impeller plate spins rapidly, shredding the food into tiny pieces. 

This measurably small-turned-waste can be flushed away with water through the holes. 

This is how the garbage disposal helps drain the clogged sink with stranded water. 

You probably think it works just like a blender. On the contrary, it doesn’t, even though it sounds like it. 

A garbage disposal works differently and doesn’t have blades. Instead, the impellers or lugs mounted on a spinning plate continuously force food waste particles against a stationary grind ring. 

The grind ring is responsible for shedding the waster into very fine particles —virtually liquifying them. 

Afterward, the running water flushes the food particles in the grind ring out of the disposer, then into your wastewater pipe. 

This waste then travels to a wastewater treatment plant or your septic system. That is how a garbage disposal work! 

However, if the sink doesn’t drain even when the disposer is on, chances are it is either jammed or clogged. 

Why Sink Only Drains When Garbage Disposal Is On? (Fix it Now!)

Sink Only Drains When Garbage Disposal Is On
Credits: Steve Cukrov/Shutterstock

When the kitchen sink only drains when disposal runs, it hampers your kitchen operations. 

And this can be annoying, knowing the hassle behind rinsing your dishes and having to deal with draining large debris into your sink.

As I said, you have o call in a plumber. With few household tools and some detective work, you can be on a rescue mission. 

There are three significant reasons why your sink only drains when the garbage disposal is on. It is either faulty plumbing, a pipeline clog, or a lack of proper venting. 

1. Faulty Plumbing

This is a rare case. But if the installer has little or no experience with plumbing and makes mistakes, the faulty connection could prevent the free water flow from the sink. 

Here are two case scenarios: 

  1. The Drain Pipe That Goes Into The Wall Is Higher Than The One From The Disposal Water Drain.

While I was often in plumbing service, this is a typical installation mistake in most homes. 

The garbage disposal outlet MUST sit higher than the drain pipe that goes into the wall —always! 

If the reverse were to be the case, especially on deep sinks, this installation pattern would alter the natural flow of water. 

Thus, causing blockage unless pushed manually or whenever you are on the garbage disposal. 

Even if you clear the clog, it will happen again and again. The best and easiest solution I have seen is removing the garbage disposal. Then connect the pipes directly. 

Get a garbage bin instead for your food waste.  

  1. The Depth Of The P-Trap Is Much

The p-trap usually sits between the drain pipe that travels into the wall and the garbage disposal pipe. 

Its main duty is to prevent clogging by trapping debris and food waste from the sink in the drain pipes. 

However, when the depth is too much, it does the opposite —trapping food waste in the drain pipe by preventing water from draining.

While there is no definitive guide for picking the right p-trap height, try changing the p-trap to a standard height and see if the water drains properly. 

2. Inappropriate Venting

For your plumbing system to work efficiently, there must be proper venting —if not, it could slow the sink drain. 

Most sink drains come with a Studor Vent. If yours does, check for any blockage. You never know if debris could accumulate in the vent, blocking airflow. 

Besides, Studor vents are user-friendly —accessible to open, clean, and replace. However, if you don’t have Studor Vents and suspect the drainage issue resulted from improper venting, install one. 

Call a professional plumber if you don’t know how to do it. 

Clog Is A Problem That Makes Sinks Stop Working

Credits: Igal Vaisman/Shutterstock

The number one problem that makes sinks stop working is clogs in the garbage disposal or the drain pipes. 

Clogging in the drain pips or garbage disposal is another reason your kitchen sink only drains when disposal runs.

The clogs may not be as serves as it sounds. This is why, most of the time, that allows water to pass sluggishly to the garbage disposal when on. 

The correct this, you must do the following; 

1. Inspect The P-Trap

Once you notice signs of clogging, the first line of action is to examine the p-trap. 

Remove it and see if there is a free flow of water. Don’t flood the kitchen; ensure there is a bowl underneath it. 

Two take away here: 

If the water drains smoothly, the clog is from the pipeline that travels into the wall; However, if it doesn’t, the clog is from the disposer.

2. Unclog The Disposal 

You must clean your garbage disposal spike and span from the food waste residues blocking water from running through the tiny holes in the shredder rings. 

Professional plumbers solve this problem by throwing loads of ice cubes into the garbage disposal to grind.

 You need to fill it. Then run hot water and then on the disposer. 

While doing this, ensure the p-trap is still open with your bowl or buck underneath it. 

3. Clean The P-Trap And The Drain Pipes 

Break out the plumber’s snake and clean the p-trap and the drain pipes. Snake them as far as you can to ensure they are clean. 

Lastly, recouple everything and check.

Refit the pipes, flood the sink, and check if it drains without flipping on the disposer. 

If the problem persists, the chance is the clogs are further down the drain pipes that goes into the wall. 

At this juncture, you should seek out professional help. 


So those are the reasons why your sink only drains when garbage disposal is on, and how to fix it. 

While this might be a surefire way always to rescue your clog sink, prevention is better than medicine. 

Here are a few don’t about the garbage disposal and sink relationship you should jot down before leaving: 

You shouldn’t run the disposal without water. Also, leaving waste to sit inside isn’t ideal. 

Do not put starchy food down the drain like rice, pasta, potato, and whatnot. On top of that, grinding fibrous materials like asparagus, artichokes, or carrots will cause you problems in the long run.

Avoid sharp or hard-like materials such as coffee grounds, seeds, or bones.

And more importantly, NEVER put your hands down to remove a jam. 

Stay safe!

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