Install a Garbage Disposer, Step by Step

The household garbage disposer is easily one of the Twentieth Century's greatest marvels. This one piece of kitchen equipment single handedly revolutionized both the cooking experience and the food waste removal industry.

A monster underneath the sink, it literally rips food waste to shreds and allows it to flow down the drain. If you don't have one, what have you been waiting for? Once you install one of these incredible machines, you'll wonder how you ever got along without it.

Whether you're replacing an old garbage disposer or installing a new one, it's an easy job. You don't need to be a master plumber or a licensed electrician to complete the job effectively. It does help if you know a little bit of each, but it's not necessary. That's what we're here for.

One prerequisite for installing a garbage disposer is a dedicated outlet under the sink. It needs to be protected by a 120 volt, 20 amp circuit breaker. An important note - a GFCI outlet will not allow the disposer to work. It must be a regular outlet. Turn the power off to the outlet before you begin, for safety.

Some tools you will need for this job include:

  • A bucket and some rags
  • Plumbers putty
  • Putty knife
  • Screwdrivers
  • Hammer
  • Wire strippers
  • Wire nuts and electrical tape
  • Pipe wrench or tongue and groove channellocks

1. After cleaning out everything under your sink, the first step is to remove the existing strainer from the sink. Under the sink, place the bucket under the "J" trap. Use the pipe wrench or channellocks to loosen the slip nuts and remove the "J" trap. Dump the water in the bucket.

2. With the "J" trap removed, look for the large nut that holds the strainer in place. Remove the nut.

3. Remove the strainer and clean up any old plumbers putty that was left behind. You may need to use the putty knife to pry the strainer up to remove it. It's important that the sink be totally clean of old putty and debris.

4. The next step is to open the new garbage disposer and install it. The first piece you'll need is the sink flange and mounting assembly. The mounting assembly consists of an upper mounting ring, a lower mounting ring and the mounting bolts. Take a nice amount of plumbers putty and form a ring around the drain. Take the sink flange and set it in the drain. Press it down slightly onto the putty.

5. Under the sink, take the gasket and mounting ring and slide them up the flange. You may need a second pair of hands to keep the flange stable on the top side. There should be a snap ring that you can connect to the flange to keep the gasket and ring secure.

6. Tighten the mounting bolts to bring everything together. There are three bolts, and it's important to tighten them evenly through the process. As the mounting assembly tightens, plumbers putty will squeeze out from under the flange in the sink. That's OK - simply wipe the excess away.

7. Now it's time to wire the disposer. On the bottom side of the disposer you should see 1. a red reset button, 2. a flywheel turning wrench hole, and 3. the cover plate for the electrical connections. Remove the cover plate. You should see a trio of wires - a black, a white and a green (or bare copper in some disposers).

8. The garbage disposer kit should include the cord and plug, so remove it from the box. The wires should be pre-stripped, but if they're not, use the wire strippers to remove about 3/4" of insulation. The side of the disposer should have a hole with a romex connector already in place. Slide the cord through the hole so that the black cord sheath is under the connector's metal. Tighten down the bolts on the romex connector to hold the wire in place.

9. Use the wire nuts to make the necessary wire connections (black to black, etc.). Secure the wire nuts with electrical tape and neatly stuff the wires back into the chamber. Replace the electrical cover.

10. If you do not have an installed dishwasher, you can proceed to the next step, but if you do have one, then there's an extra step. On the side near the top of the disposer you will see a close-ended tube coming out the side. That is where the dishwasher inlet line gets hooked up to. Simply take a screwdriver and hammer and chisel out the plug. It will usually fall into the disposer, so just turn the disposer over and the piece of plastic will fall out. If you have no dishwasher, or if you have the mobile kind that hooks directly up to the faucet, then leave the plug in place.

11. Now it's time to mount the disposer. Under the sink, line up the disposer with the mounting assembly. You will see where the three "ears" on the disposer should lift into. Once the "ears" are into the assembly, turn the disposer to lock it into place. It could take a few tries and the disposer may get heavy, so just take your time and don't get frustrated. You will feel it lock into place. You will still be able to slightly turn the disposer, but everything will get tightened down at the end.

12. Next connect the plumbing. You may need to turn the disposer slightly to line everything up. If you have a dishwasher, the drain line gets connected to the inlet port that you knocked out earlier. Odds are the "J" trap you removed earlier will not line up with the garbage disposer, so you may have to cut some PVC plumbing pipes to make everything fit correctly. Be sure to use the nylon washers at each lock nut.
Note - When connecting the pipes, make sure you slide the lock nut on the pipe first, then the nylon washer.

13. Connect the plumbing and make sure all the lock nuts are tight and that the disposer line is tight. Near the mounting assembly is a rotating cam collar. With a screwdriver or wrench for leverage, tighten the collar down. This will lock the disposer into place and solidify the installation.

14. Now check for leaks. Turn the faucets on and let water flow through the disposer. Inspect every locknut and seal for leaks. Tighten anything that needs it. Turn your dishwasher on and make sure the connection to the disposer doesn't leak. If everything stays dry, you're good to go.

15. Turn the power back on to the under sink outlet. Plug the disposer into the outlet and with the water running, hit the switch. You should hear the beautiful humming of your new disposer.
Note - Never run the disposer without the water running.

Congratulations! You just installed your very own garbage disposer. If you would like to learn a little about how the garbage disposer works, or if you ever need some troubleshooting tips, please check out this companion article.