How to Install a Garbage Disposal

Installing a Garbage Disposal

A typical garbage disposal unit lasts about 12 years, so if it's a feature you want in your kitchen, there is every likelihood that you'll need to replace it at some point. Or, you may want to install one for the very first time when remodeling an old kitchen

If you are installing one for the first time, be aware that there are some wiring and plumbing skills necessary—work you may want to have a professional do if you're not fully confident of your skills. For example, most current building codes require a dedicated 20-amp 120-volt outlet under the sink near the disposal. The outlet will need to be controlled by a switch that is accessible to a user standing at the sink. There is a good chance that this circuit is already in your kitchen, but if it's not, you'll need to have this circuit installed before you can install the disposal. 

A Garbage Disposal Isn't Always Needed

Before you automatically replace a failed disposal or buy one for a kitchen remodel, make sure you need it. 

Initially, garbage disposers were regarded as luxury items, but gradually they became a common feature of almost all kitchens—so much so that people may automatically assume a kitchen needs one. Today, though, environmental concerns are prompting some movement away from garbage disposals.

The amount of raw organic garbage pumped into city sewer systems through kitchen sink drains is putting a considerable strain on waste treatment facilities. As a result, some communities have even gone to the length of outlawing disposals, while others are considering the move. Many communities recommend that organic wastes are best thrown away in the standard trash rather than ground up and flushed down the sink. And there are gradually more and more communities offering organic waste programs designed to pick up "wet" wastes and compost them. If your community offers any such program, there is no reason whatsoever to install a garbage disposal. 

A garbage disposal is a very bad idea if you live in a rural area where wastewater is processed by a septic system and drain field. You absolutely should not flush organic kitchen wastes into a septic system, as it will greatly complicate maintenance of the system and prevent the system from breaking down wastes efficiently.

If you are quite sure you want and need a garbage disposal, though, the following steps will show how to install one. 

Tools & Materials You Will Need

  • New garbage disposal
  • Garbage disposal mounting ring and drain fitting
  • Plumber's putty
  • Channel-type pliers
  • Screwdrivers
  • Hammer
  • Plug in power cord
  • Drain pipe extension pieces (if necessary)

Disconnect the Power and Remove the Old Garbage Disposal

Garbage Diposal
  1. The power must be disconnected from the old disposal before you remove it. This may be as simple as unplugging it from its electrical outlet, but if the disposal is "hardwired" directly into circuit wiring, as is the case in some older installations you'll need to first shut off the circuit at the main service panel. You do this by going to your electrical service panel and either removing the fuse or turning off the circuit breaker feeding power to the unit.
  2. If there is not a dedicated circuit and outlet for the disposal, now the time to have an electrician install one. 
  3. Remove the garbage disposal by disconnecting drain connections attached to the disposal, then disconnecting the disposal from the flange assembly. 
  4. Remove the disposal flange assembly from the sink drain. Although it is sometimes possible to use the same flange assembly if you are replacing the old unit with a new one from the same manufacturer, it is usually best to replace these parts to ensure a good drain seal.

Install the Drain Fitting and Mounting Ring

Garbage disposal mounting assembly

To install the garbage disposal, you first need to install the assembly that will hold it in place beneath the sink. This is a special form of drain fitting that consists of a drain flange and mounting ring that sandwiches around the top and bottom of the sink drain opening. 

  1. Seal the sink opening by placing a 1/2-inch-thick bead of plumber's putty around the drain opening from inside the sink.
  2. Insert the new disposal drain flange into the sink opening and press it firmly into the plumber's putty.
  3. Have someone hold the drain flange in place from the top as you now work from under the sink. Take the fibrous gasket and triangular attachment ring and slide them onto the tailpiece of the drain fitting.
  4. Secure the ring by snapping the round clip spring or snap ring into the groove on the drain fitting. 

Tighten the Mounting Ring Assembly

garbage disposal sink flange
  1. Tighten down the mounting assembly by tightening the three mounting screws, rotating between them to gradually apply even pressure. Tighten the screws until the drain flange is tight against the bottom of the sink and plumber's putty has oozed out around the drain opening. Take care not to overtighten; it's possible to squeeze out all the plumber's putty that must be present to complete the seal. 
  2. Wipe away the excess plumber's putty around the drain opening inside the sink, using a rag.

Connect the Disposal's Power Cord

Garbage disposal bottom diagram

Before mounting the garbage disposal, you'll need to attach its plug-in power cord.

  1. Remove the electrical plate found on the bottom of the disposal unit.
  2. Using wire nuts, connect the white lead from the disposal to the power cord white wire, the black lead to the black cord wire, and the green ground lead to the green ground wire.​
  3. Tuck the connected wires into disposal electrical box and replace the cover plate.

Optional: Dishwasher Connection

Dishwasher inlet connection pipe

In some installations, the dishwasher drain water is run through the garbage disposal. If that is your case, proceed as follows:

  1. Located near the top of the disposal chamber you will find a dishwasher inlet. Using a screwdriver, take a hammer and knock out the plug.
  2. Remove the knock-out plug inside the dishwasher nipple on the disposal unit.

Mount the Garbage Disposal

An In-Sink-Erator garbage disposal

The disposal can get a little heavy while doing this step so be careful you don't strain yourself:

  1. Align the disposal by lining up up the top collar on the disposal with the three mounting ears on the sink mounting assembly.
  2. While holding the disposer in place, rotate the top collar so that the three mounting ears engage into the mounting collar on the bottom of the drain fitting. 

Connect the Drain Lines

A garbage disposal
  1. Fasten the rubber discharge tube to the disposal unit with its gasket and screws.
  2. Position the disposal by turning it so that the discharge tube aligns with the sink drain waste trap. You may need to add extension pieces or shorten the pipes to make the proper connections. It is important that these connections be well made and tight.
  3. Once the drain connection is made, connect the dishwasher line, if it is present Slide the dishwater hose onto the disposal nipple, and secure it with whatever clamp is provided by the manufacturer. 

Lock the Garbage Disposal Unit in Place

Disposal mounting ring

Firmly lock the disposer to the sink mounting assembly by tightening the rotating cam collar on the disposal, using either a screwdriver for leverage ​or a special wrench that may have come with the garbage disposal for this purpose. You likely will feel a distinct "click" as the disposer locks into place.

Check for Leaks and Proper Operation

Kitchen sink draining
  1. Turn on the water and run it through the disposal to check all connections for leaks.
  2. If there are leaks, tighten any loose drain connections
  3. Plug in the disposal to the wall outlet and make sure the circuit power is turned on. 
  4. Test operation of the garbage disposal by running the motor while flushing water and some organic material through the drain.