How to Install a Garbage Disposal for the First Time

Begin by ensuring the work area is safe and prepared. Turn off the corresponding circuit breaker in your home's electrical panel that powers the outlet under the kitchen sink. Use a voltage tester to confirm there is no power to the outlet. Clear out all items from the cabinet under the sink to create ample workspace. Place a bucket directly under the P-trap and drain pipes to catch water, and lay down old towels to absorb any spills.

Using a pair of channel-lock pliers, loosen the large slip nuts that connect the P-trap (the U-shaped pipe) to the sink's tailpiece and the drain arm extending into the wall. Once the nuts are loose, you should be able to unscrew them by hand. Carefully wiggle the P-trap free and empty any remaining water into the bucket. Then, remove the horizontal drain arm from the wall pipe.

From underneath the sink, use pliers or a strainer wrench to loosen and remove the large mounting nut holding the sink strainer in place. There may be screws to loosen as well. Once the nut is off, push up on the strainer from below to pop it out of the sink drain opening. Use a plastic putty knife to scrape away all of the old, hardened plumber's putty from the sink's surface. Clean the area thoroughly with a rag and a cleaning solvent if necessary.

Before mounting, prepare the disposal unit. First, install the power cord. Turn the disposal upside down, remove the electrical cover plate with a screwdriver, and connect the wires from the power cord kit to the disposal's wires (black to black, white to white, green to green ground screw) using wire nuts. Secure the cord with the strain relief clamp. Next, locate the dishwasher inlet port on the side of the disposal. Insert the tip of a flathead screwdriver into the opening and strike it firmly with a hammer to knock out the plastic plug. Reach inside the disposal's grinding chamber and remove the dislodged plug.

Take a small amount of plumber's putty and roll it into a snake-like rope about 1/2-inch thick. Press this rope firmly around the underside of the new sink flange (the metal drain piece). From the top of the sink, press the flange down securely into the drain opening, so the putty oozes out. From underneath the sink, slide the fiber gasket, then the backup flange, and then the mounting ring over the bottom of the sink flange. Secure it by attaching the snap ring. Finally, tighten the three mounting screws evenly and firmly with a screwdriver. This will pull the assembly tight against the sink. Wipe away the excess putty from inside the sink with a rag.

This step can be awkward due to the weight and position of the disposal. Lift the garbage disposal unit up to the mounting ring. Align the three mounting tabs on the disposal with the ramps on the mounting ring. Push the disposal up and turn it clockwise until the tabs lock firmly into place over the ridges on the mounting ring ramps. You should feel it lock in. You can use the small wrench often supplied with the disposal (or a pair of pliers) to insert into a mounting lug for extra leverage to turn and tighten it fully.

First, connect the drain discharge tube. Place the rubber gasket inside the disposal's discharge outlet, then attach the L-shaped discharge tube with the metal flange and two screws. Next, connect the dishwasher drain hose to the dishwasher inlet you prepared earlier. Slide a hose clamp over the hose, push the hose onto the inlet, and tighten the clamp securely with a screwdriver. Finally, assemble the new P-trap. You may need to dry-fit the pieces and cut the pipes to the correct length with a hacksaw or tubing cutter to align properly between the disposal discharge tube and the drain pipe in the wall. Once sized, connect all pieces and hand-tighten the slip nuts, followed by a quarter-turn with channel-lock pliers.

With everything connected, it's time to test your work. Plug the disposal's power cord into the switched outlet under the sink. Place the sink stopper in the drain and fill the sink basin about halfway with cold water. Lay dry paper towels on the bottom of the cabinet under all the new pipe connections. Now, remove the sink stopper to let the water rush down, and immediately turn on the wall switch for the garbage disposal. While the water is draining and the disposal is running, use a flashlight to carefully inspect the sink flange, dishwasher connection, discharge tube, P-trap, and all slip nuts for any signs of dripping. If you find a leak, turn off the disposal and water, and tighten the leaking connection slightly.