How a Garbage Disposal Works & Everything Else

What is a garbage disposal and how does it work?

A garbage disposal is an electrically powered appliance installed underneath the kitchen sink between the drain opening and the P-trap. It grinds food waste into tiny pieces which are then washed down the drain line with the help of cold water from the faucet.

If you ask most people, they will tell you that a garbage disposal works pretty much like a blender.  Is that correct though? The simple answer is NO.

InSinkErator garbage disposal sectional view

A garbage disposal works by spinning food waste inside a grinding chamber where it is shredded into tiny pieces and washed down the drain line. You always run a garbage disposal with a stream of cold water flowing into it to wash down the grinded food down the drain line to prevent clogs.

Garbage disposals are installed underneath the kitchen sink between the drain opening and the drain trap also called a P-trap. It also has an inlet opening which allows you to connect it to the dishwasher.

A P-trap is the U-bend under the kitchen sink. It traps potential clogs preventing them from clogging the drain line further away where unclogging would be more difficult. Due to its shape, it is also full of water which acts as a barrier preventing sewer odors from coming up through the sink drain.

Since a garbage disposal is installed directly below the kitchen sink drain opening, its waste flows out through the sink’s drain line. The sink drain line is then connected to the house main drain stack which in turns drains into the sewer line outside your house. Your sewer line is then connected to the city’s sewer lines or septic tank.

There are 2 types of garbage disposals. These are batch feed and continuous feed garbage disposals.

In a batch feed garbage disposal, waste is grinded in batches. You the put waste inside the unit and then start it and let it run until all the waste has been grinding before adding more waste.

Continuous feed garbage disposals are just like their name implies. Once you start a continuous batch garbage disposal, you can add waste into it continuously wile it is running until you are done grinding.

How a Garbage Disposal Works Diagram


How Do Garbage Disposals Work

Most of the work happens inside the garbage disposal. To understand how garbage disposals work, you should however start with the outside. What you can see.

From the top of the sink where waste and water are feed into the garbage disposal, there a rubber flaps which cover the opening. That is called the splash guard. It prevents water from splashing around when the garbage disposal is running.

If you have a dishwasher, it will be connected to the garbage disposal from the very top of the unit. Please note that the disposal’s garbage disposal inlet comes with a plug that should be knocked out before it is connected.

Failure to remove the knock plug will result in a dishwasher that is not draining or one that is leaking from the air gap.

On the bottom side of the garbage disposal is where the drain line is connected. If you have a double kitchen sink, the 2 sinks will share a single drain line and are connected using a piece of pipe called a tee.

Most importantly, you will see a power cord connected to the bottom of the garbage disposal from a nearby electrical outlet. Garbage disposals need 120 volts of power to run.

A garbage disposal is made of 2 halves comprising the upper hopper and lower chamber, connected together using a clamping ring. The upper hopper is where the grinding takes place while the lower chamber is where the motor is housed and also where the waste outlet is located.

If you look inside a garbage disposal after removing the splash guard, you will see 2 impellers which are curved. These impellers are mounted on the sides of what s called the flywheel.


The flywheel is connected to the motor using a shaft. In essence, as the motor spins, the motion is delivered to the flywheel by the motor shaft

Also inside the upper hopper chamber is a stationary metal ring with teeth and grooves called a shredder ring. This ring is responsible for grinding food waste into tiny pieces which can wash down through the holes in the chamber.

When you start the garbage disposal, the flywheel starts to spin creating a centrifugal force that spins the food scraps and water inside the upper hopper, forcing them against the shredder ring where they are shredded into tiny pieces.

The function of the impellers is to push the food waste against the shredder ring and not grind it themselves as it is generally thought.

The main reason it is important to run cold water as you are grinding food waste is to help wash the grinded food out of the disposal and into the drain line. This also helps to prevent the garbage disposal or drain line from clogging.

Things You Shouldn’t Put in a Garbage Disposal

While garbage disposals are quite effective in grinding waste, not all types of waste should be put inside it. You still need to have a trash can.

The following are some of the things that you shouldn’t put inside a garbage disposal:

  • Nuts and shells
  • Fibrous vegetables/fruits
  • Potato peels
  • Coffee grounds
  • Pasta, rice, bread and basically starch
  • Animal bones
  • Oatmeal
  • Onion skins
  • Pits and seeds
  • Fats, grease and oils
  • Broken glass

The above items will either jam the garbage disposal impellers meaning they can’t spin, or clog it and as a result it will not drain.

I also cannot overemphasize the need to run cold water as you grind waste with your disposal. The water forms a slurry with the grinded food waste allowing it flow out without clogging both the disposal and the drain line (especially the P-trap)

Avoiding Smells in a Garbage Disposal

A smelly garbage disposal is not pleasant. If not taken care of, garbage disposals can get very smelly. This is often caused by trapped food waste inside the chamber which decomposes resulting in odors.

A really nice way to clean a garbage disposal is to fill it with ice cubes and add about a ¼ cup of salt. Turn on the water and start the garbage disposal.

As the ice cubes and salt are spun inside the chamber, the scrape off any food particles trapped inside and flush them down the drain line.

To leave your garbage disposal smelling fresh, cut small slices of lime and drop on at a time inside the garbage disposal.

Troubleshooting a Garbage Disposal

Garbage disposals will develop problems from time especially when they are older. The following are the different garbage disposal problems and how to fix them.

1. Garbage Disposal Won’t Turn On

When a garbage disposal won’t turn on, it is a sign that it is not receiving power. This is often caused by a tripped reset button.

A garbage disposal reset button is a small (usually red) button located on the bottom or lower back of the disposal. It is also called an overload protector button.

In case the garbage disposal is overloaded, clogged, it has been running for a long time, the impellers are jammed among other issues, the reset button trips cutting off power supply to the unit.

To reset your garbage disposal, turn off and unplug it from the switch. Press in the reset button and then plug it in and start the disposal. If the garbage disposal reset button won’t stay in, wait for 10 minutes then try again. For more information on resetting a garbage disposal check out this post.

2. Garbage Disposal Hums

If your garbage is humming, it means that it is receiving power but the impellers are not spinning. This is usually caused by jammed impellers.

Turn off the garbage disposal and unplug it. Grab a flashlight and check if there is something jamming the impellers like a spoon, folk or knife. Pull it out.

If there is nothing you can see, try to manually spin the impellers. Use the garbage disposal wrench and turn it clockwise and counterclockwise to free the impellers.

If you do not have a garbage disposal wrench you can use a ¼-inch hex wrench or rotate the blades from the sink opening using a wooden stick.

Plug in the garbage disposal and check if the humming stops after that. If not it may be broken or badly clogged.

3. Clogged Garbage Disposal

Garbage disposals get clogged. The first thing you should try and find out is the location of the clog. What I like to do is to disconnect the drain line from the garbage disposal to the trap and check inside.

You will find a lot of gunk there which prevents the garbage disposal from draining. If you have a double kitchen sink where both sinks are not draining, the clog is usually the P-trap or beyond.

After cleaning the P-trap, I then pour half a cup of baking soda inside the garbage disposal followed by a cup of vinegar. I let them fizzle inside the unit for about 10 minutes.

After that I flush the garbage disposal with hot water for 30 seconds followed by cold water. Check out this post for more information on how to unclog a garbage disposal.

And that’s pretty much it about garbage disposals. I hope this post was helpful

Leave a Comment