How to Install a Garbage Disposal

Turn off the circuit breaker that powers the under-sink outlet and verify it's dead with a non-contact voltage tester. If replacing an existing disposal, unplug it (or disconnect the hardwired cable), loosen the discharge tube clamp, disconnect the dishwasher hose if present, then twist the lower mounting ring counterclockwise to release the unit. If you're installing fresh into a standard drain, place a bucket under the P-trap, loosen the slip-nut fittings with channel-lock pliers, and remove the drain tailpiece, P-trap, and the old sink strainer from above.

Roll a rope of plumber's putty about 1/2 inch thick and 10 inches long between your palms. Press it around the underside of the new sink flange's lip in a continuous ring. From above, push the flange into the sink drain opening and press it firmly so putty squeezes out evenly around the rim. Don't clean up the excess putty yet — it will be trimmed after the mounting assembly is tightened from below.

Working from underneath the sink, slide the fiber gasket, the metal backup flange, and the mounting ring up onto the sink flange's sleeve in that order. Push the snap ring up and into the groove on the sleeve — you'll hear it click into place, which locks all the hardware against the underside of the sink. Tighten the three mounting screws on the mounting ring evenly, alternating between them a few turns at a time, until the backup flange is pulled snugly against the sink bottom. From above, trim the excess plumber's putty with a putty knife.

If you have a dishwasher that drains through the disposal, locate the dishwasher inlet on the side of the disposal — it's a small circular knockout plug inside a short nipple. Place a flathead screwdriver or a wooden dowel against the knockout and tap it firmly with a hammer to pop it out. Reach into the disposal with pliers and remove the loose plastic disk — if you leave it inside, it will jam the grinding plate on first use. If you do not have a dishwasher, leave the knockout in place.

If your disposal came with a factory-installed power cord, skip to the next step. Otherwise, remove the electrical cover plate on the bottom of the unit (one or two screws). Feed the power cord (or the Romex cable from the wall) through the strain-relief clamp. Connect the black wire to the black wire, the white wire to the white wire, and the green ground wire to the green ground screw on the disposal using wire nuts. Tug each connection to confirm it's tight, tuck the wires into the compartment, and replace the cover plate.

Lift the disposal and align its three mounting tabs with the slide-up ramps on the mounting ring underneath the sink flange. A stack of books or an overturned bucket under the disposal helps support its weight while you work. Rotate the lower mounting ring clockwise using the included wrenchette (a small Allen-wrench-like tool that fits into a lug on the ring) until all three tabs lock into position and the unit hangs firmly from the flange assembly. Give the disposal a gentle tug downward to confirm it's locked — it should not budge.

Attach the rubber gasket to the discharge outlet on the side of the disposal, slide the discharge tube into the outlet, and tighten the metal clamp with a flathead screwdriver. Connect the other end of the discharge tube to the P-trap using a slip-nut fitting — hand-tighten first, then snug it with channel-lock pliers (a quarter turn past hand-tight). The discharge tube should slope gently downward toward the P-trap — if it runs uphill at any point, water will pool and drain slowly. If connecting a dishwasher, clamp the drain hose onto the dishwasher inlet nipple with a hose clamp.

Plug the disposal into the outlet (or turn the breaker back on for hardwired units). Turn on the cold water and let it run for 30 seconds while you inspect every connection point with a flashlight: the sink flange from above, the mounting assembly, the discharge tube clamp, all P-trap slip-nut joints, and the dishwasher hose clamp. Dry each joint with a paper towel, then check again — even a tiny drip needs to be tightened now. With the water running, flip the wall switch to turn on the disposal and listen for smooth operation with no rattling or grinding sounds.