How to Replace a Garbage Disposal

A garbage disposal is one of those appliances you take for granted until it doesn't work. It's a luxury-turned-necessity in busy households, providing a convenient way to deal with messy food scraps. So if your old disposal literally doesn't cut it, you can replace it with a new one.

Do It Yourself or Hire a Pro?
A plumber will charge about $300 to replace an old garbage disposal if the plumbing and electrical connections are identical. If you have some plumbing and electrical experience, you can do it yourself for the cost of a new unit around $100. The project takes about four hours, but the working conditions are less than ideal. It can be uncomfortable working in the confined space under a sink. Still, a direct replacement is a relatively straightforward project that can save you a few bucks.

If you decide to do it yourself, look closely at the old unit before you remove it to see how it's hooked up. Note the diameters of existing pipes and collars (an inexpensive caliper will measure pipe dimensions easily and accurately), the number and placement of bolts, and how the disposal is attached to the drainpipe. In short, look at all the parts and the way they connect. Then make a rough sketch of the electrical connections, and you'll be properly armed when you go shopping for your new disposal.If the new disposal's plumbing and/or electrical connections are different from the old one's, we recommend hiring a pro. Adding new plumbing or wiring can greatly complicate a job. Step by Step
1. Disconnect the power. Turn off the power to the disposal by pulling the fuse or switching off the circuit breaker that controls the unit. Most disposals have power cords that run from the underside of the disposal to a switch-controlled outlet under the sink. To be sure the power is off, we prefer to run the disposal while a helper at the main service panel locates the right fuse or circuit. When the circuit is shut off, the disposal will stop.

If the outlet under the sink is corroded or otherwise in bad repair, we suggest hiring an electrician to replace it. You can't be too careful when electrical connections are near water. 2. Remove the disposal. Use a pipe wrench, a large adjustable wrench or a large pair of tongue-and-groove pliers to undo the slip fittings on the P-trap, and release the trap's contents into a bucket. (You may also find a cleanout plug on the underside of the pipe.) Once the P-trap is drained, remove hose clamps, discharge tubes and any other fittings that connect the old disposal to the drainpipe.Hold the disposal from underneath with one hand while you loosen the screws on the side of the mounting assembly. (The disposal probably came with a special tool for those screws, but chances are you won't be able to find it. In that case, use a screwdriver.) Turn the assembly counterclockwise to release the disposal from its mounting.

3. Disconnect the disposal's electrical wiring. Once the disposal is disengaged, remove the screws securing its electrical cover plate, which is usually on the bottom of the unit. Then, to be doubly sure that the power is off, carefully remove the wire connectors that join the wires inside, and use a voltage tester to test individual wires. If there's no current, pull the wires apart and loosen the clamp that holds the electrical cable. Pull the cable out of the unit.

4. Remove the old mounting ring and sink flange. Use a screwdriver to pry off the snap ring on the old mounting assembly, and remove the screws that connect the mounting ring to the sink flange. Pull the mounting ring away from the sink flange and remove any backup rings, gaskets or other parts of the mounting assembly.

From above, pry the sink flange out of the drain hole. Clear any remaining plumber's putty, old sealing gaskets or other debris from the area before you install the new hardware.

5. Disassemble the new disposal hardware. Most new disposals are shipped assembled, so you have to disengage the mounting assembly from the body of the disposal, then pry the snap ring off of the mounting ring with a screwdriver. This should unlock the separate pieces of the mounting assembly. If you have trouble with this step, consult the manufacturer's directions.

6. Install the mounting assembly. With your hands, roll a generous amount of plumber's putty into a snake and apply it around the rim of the sink flange where the rim meets the sink drain hole. From above the sink, press the flange into the drain hole.From underneath the sink, install the gasket, the backup ring if one comes with your model, the mounting ring and the snap ring over the neck of the sink flange. Tighten the screws on the mounting assembly, alternating screws as you tighten, until the ring is uniformly secure. Then, from above, remove any excess putty from around the flange seal.

7. Make the electrical connections. Remove the electrical cover plate on the new disposal. Insert the power cable at least 6 inches into the disposal's cord connection slot and tighten the clamp screws. Pull the cord's wires and the unit's wires together inside the disposal's electrical box. As needed, strip and splice the white wires to white and black to black using wire connectors. Connect the green ground wire to the grounding screw on the disposal, then replace the cover plate.

8. Connect the discharge tube to the disposal. Use the hardware provided to attach the discharge tube to the discharge outlet on the side of the disposal. 9. Mount the disposal. Hold the disposal up against the mounting assembly, and turn the mounting ring clockwise until the disposal locks into place. Tighten the screws on the mounting assembly with a screwdriver or the tool that comes with the disposal. Rotate the disposal so that the discharge tube can be easily connected to the drainpipe.

10. Install the plumbing. Connect the disposal to the P-trap and the trap to the drainpipe. (The layout of your drain assembly may vary, depending on space constraints and whether you have a one- or two-bowl sink.) Tighten the parts by hand, then finish the job with a pair of tongue-and-groove pliers.

When all the plumbing is in place, run water through the disposal to test for leaks and tighten the connections on any loose joints. Plug the disposal's power cord into the switch-controlled outlet that the old disposal was connected to, and turn the power back on. Use any available food scraps to make sure that the disposal works properly.

Tip From the Pros
Feed a lemon through the disposal once a month to keep it smelling fresh.