How to Install a Garbage Disposal

Remove the Old Disposal

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.

Remove the garbage disposal by disconnecting drain connections attached to the disposal, then disconnecting the disposal from the flange assembly. 

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

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 sink flange and mounting ring that sandwiches around the top and bottom of the sink drain opening. 

Seal the sink opening by placing a 1/2-inch-thick bead of plumber's putty around the drain opening from inside the sink. Insert the new disposal sink flange into the sink opening and press it firmly into the plumber's putty.

Have someone hold the sink flange in place from the top as you work from under the sink. Take the fibrous gasket and triangular attachment ring and slide them onto the tailpiece of the sink flange.

Secure the ring by snapping the round clip spring or snap ring into the groove on the flange tailpiece.

Tighten the Mounting Ring Assembly

Tighten down the mounting assembly with the three mounting screws, tightening each a little bit at a time to gradually apply even pressure. Tighten the screws until the sink flange is tight against the bottom of the sink and excess 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. 

Wipe away the excess plumber's putty around the drain opening inside the sink, using a rag.

Connect the Disposal's Power Cord

Before mounting the garbage disposal, you'll need to attach its plug-in power cord. Remove the electrical cover plate found on the bottom of the disposal unit. Install a strain relief fitting in the hole that the power cord will go through, and tighten the fitting nut with pliers.

Feed the loose-wire end of the power cord through the strain relief, and tighten the strain relief clamp onto the cord with a screwdriver. Using wire nuts, connect the white lead from the disposal to the power cord's white (neutral) wire, the black lead to the black (hot) cord wire, and the green ground lead to the cord's green ground wire.​ Tuck the connected wires into the disposal's electrical box and reinstall the cover plate.

Prepare for a Dishwasher Connection (optional)

In some installations, the dishwasher drain water is run through the garbage disposal. If that is your situation, locate the dishwasher inlet nipple near the top of the disposal chamber. Insert a screwdriver into the nipple, and tap the screwdriver with a hammer (like a chisel) to knock out the plug inside the nipple. The plug is a plastic disc that will fall into the disposal's grinding chamber. Reach inside through the top of the disposal unit and pull out the disc.

Mount the Garbage Disposal

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

Align the disposal by lining up the top collar on the disposal with the three mounting ears on the sink mounting assembly. While holding the disposal 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

Fasten the rubber discharge tube to the disposal unit with its gasket and screws. 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.

Once the drain connection is made, connect the dishwasher line, as applicable. Slide the dishwater hose onto the disposal nipple, and secure it with the clamp provided by the manufacturer. 

Lock the Garbage Disposal Unit in Place

Firmly lock the disposal 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 disposal locks into place.

Check for Leaks and Proper Operation

Turn on the water and run it through the disposal to check all connections for leaks. If there are leaks, tighten any loose drain connections. Plug in the disposal to the wall outlet and make sure the circuit power is turned on. 

Test the operation of the garbage disposal by turning on the water and disposal and dropping some food scraps into the drain.