How Garbage Disposals Work

How to Wire, Install or Replace a Garbage Disposal

Wiring, installing or replacing a garbage disposal may, at first, appear to be a daunting task, but with the right tools and a little know-how, it can be as simple as grinding up last night's mashed potatoes.

Garbage disposals are truly the unsung heroes of the kitchen. You may not think much of them if you don't have one installed, but once you begin utilizing your garbage disposal, it'll be hard to know how you ever managed without it. They gladly swallow up your leftovers and other kitchen undesirables and they never moan or groan about what kinds of things you feed it. So, with a little bit of preparation and some spare time, you can be on your way to living the good life--the garbage disposal life.


In order to install a garbage disposal, you have to have an available outlet that is protected by a 120 volt, 20 amp circuit breaker. Note that a GFCI outlet will not do the trick. Once the proper outlet is in place, make sure that the power is shut off, and then start gathering your tools. The required tools are: 

  • Bucket & Rags
  • Plumbers putty
  • Putty knife
  • Screwdrivers
  • Hammer
  • Wire strippers
  • Wire nuts & electrical tape
  • Pipe wrench

1. Clear everything from under your sink so that there is room to operate. The first task is to disconnect and remove the strainer and all of waste drain lines from the sink.

2. Place your bucket under the sink and remove the wastelines.  Empty all of the excess water into the bucket

3. Once the waste lines are removed, you need to remove the mounting assembly.  You should see a large nut that is securing the strainer. Remove the nut.

4. Remove the strainer and make sure to clear away any pre-existing plumbers putty from around the area. You want the surfaces to be nice and clean.

5. Now you can open your new garbage disposal and begin installing it. First off, you will need the sink flange and the mounting assembly. The mounting assembly includes upper and lower mounting rings and mounting bolts. Open up your plumbers putty and place a quarter-inch coil of putty around the drain. Next, take the sink flange, place it in the drain and press it down carefully onto the putty.

6. Find your gasket and mounting ring and head back under the sink. Take the gasket and the mounting ring and push them up the flange. Connect the snap ring to the flange, which will keep the gasket and ring in place.

7. Now it's time to tighten the mounting bolts. Locate the three mounting bolts and begin tightening them. Alternate between the three bolts, and make sure that they are evenly tightened. Plumbers putty will most likely emerge from under the flange, but there's no need to worry; just wipe away the excess.

8. Now comes the wiring. Rest the disposer on its side underneath the sink. After shutting off the breaker, you need to remove the disposal's cover plate to access the wiring. Connect the white and black wires to the matching wires from the power supply. Next ground the supply wire and replace the electrical cover plate on the unit.

9. If you happen to have a dishwasher then there is an extra step in the process. Find the close-ended tube on the side of the disposal, near the top. This is where the dishwasher inlet line is connected. Take out the line plug with a screwdriver and a hammer. The plug may fall into your disposal, so be sure that you get it out before proceeding.

10. Now you're ready to mount your disposal. Line it up with the mounting assembly under the sink. There are three tabs on the disposal that help it lock into the mounting assembly. Once the tabs are into the mounting assembly, turn the disposal so that it locks into place. This may be a bit frustrating, but be patient. You will know when it locks into place. After it is locked it will still be a bit loose. Don't fret; there's more to come.

11. Shift your disposal so that the discharge tube lines up with the water pipes. If you have a dishwasher, connect the drain line to the inlet port on the side of the disposal. Your "J" trap will probably not line up perfectly with the disposal, especially if you have a double-bowl sink. Cut some PVC plumbing pipes so that the connection fits properly. Remember to slide the lock nut on the pipe before the nylon washer.

12. Once the plumbing is connected, make sure that all of the nuts are tight and that the disposal line is secure. There is a rotating cam collar near the mounting assembly. Tighten the collar down with a screwdriver or wrench. The disposal should now be locked into place.

13. Now it's time to test your handy work. Turn on the faucets and let the water flow through the disposal. Inspect every area to ensure that there is no leakage. If you have a dishwasher, turn it on and check that connection. Tighten up any problem areas to make sure everything stays dry.

14. Restore power to the outlet under the sink and plug in the disposal. Turn on the water because it needs to be running for you to flip the switch. Always run the water when you run your disposal! You should hear the exciting sound of your lean, mean, disposing machine.  

Welcome to the world of garbage disposal living. Enjoy your new friend in the kitchen, but always respect what your disposal is capable of doing. Safety is of the utmost importance when dealing with a garbage disposal, so keep your hands and fingers clear of the opening.