Step 1: Remove Existing Drain
Turn off the water to the sink. When installing a garbage disposal, be mindful of safety. If you have an existing outlet with which to power the disposal already, you may want to deactivate power to that circuit now as well. If you do not have an existing outlet, see Step 6. Remove the existing waste (drain) pipe (or pipes, if you have a two-bowl sink) that connects at the sink strainer and at the threaded fitting at the wall or floor (the stub out). Save the piping for possible reuse if it is plastic with compression or “threaded-type” fittings. If the pipe is welded or metal, toss it. Unscrew fittings by hand or with groove-joint pliers. Use a hacksaw to cut a welded pipe.
Before starting, be sure to read the manufacturer’s instructions carefully. This is a general guide for installing a garbage disposal; your particular model’s installation may require specific steps.
Be sure you have enough room underneath your sink to install the disposal.
Place a pan or bucket under the drain trap to catch any water that may spill as you remove the drain plug, (if there is one), or disconnect the trap.
Step 2: Remove the Sink Strainer
Remove the sink strainer—the fitting secured to the sink bowl (one type is held with a large lock nut, another type with three screws). In its place, install the flange that came with the disposal. Before doing so, roll plumber’s putty between your hands until you have a long piece that will fit around the base of the flange. Then apply the putty under the flange’s lip before placing the flange firmly in the drain hole to form a seal with the sink bowl.
Step 3: Install Mounting Assembly
Install the mounting assembly gasket and mounting and retaining rings onto the flange per the manufacturer’s instructions, and tighten the screws. Start with one screw and then continue on with the others, a little at a time, until the gasket and flange are both tight to the sink bowl. Remove excess putty from around the flange inside the sink with a rag or paper towels.
Step 4: Mount the Disposal
Mount the garbage disposal to the flange according to the manufacturer’s instructions. Attach the drain elbow. If you have a dishwasher, prepare the disposal drain following manufacturer’s instructions. Slip the disposal’s slotted flange over the mounting bolts. Attach the disposal’s discharge tube, as instructed.
During garbage disposal installation you may need to connect the unit’s power cord to the unit itself. It is probably easier to make all wiring connections at this stage in the process, before mounting the garbage disposal. Be sure you have enough cable to extend to the power source (see Step 6).
Step 5: Connect Waste Pipe
Connect a two-piece tubular P-trap to the drain elbow and the drain fitting at the wall (stub out). Cut the P-trap as needed and rotate both the trap section of the P-trap and the disposal. Tighten the waste pipe fittings and the disposal, and connect any dishwasher hose to the disposal’s drain fitting with a stainless steel hose clamp.
Step 6: Connect Power
Connect the garbage disposal to a grounded 15- or 20-amp circuit, depending on the requirements of your disposal model. If you don’t have an outlet under the sink, you will need to install one or have one installed so that the unit’s power cord can be plugged in. Note that for some models, the power cord will not be already attached, so you will need to complete it yourself. Follow the manufacturer’s instructions closely when making electrical connections. Basically, you will be connecting the cord’s white wires to the disposal’s white wires, the cord’s black wires to the disposal’s black wires, and the ground wire to the disposal’s ground connection.
When installing a new under-sink outlet, choose a Ground Fault Circuit Interrupter (GFCI) outlet.
When working with any electrical circuit, disconnect power to the circuit at the main fuse box before handling any wiring, to avoid the risk of electric shock. If you’re unsure which breaker to deactivate, you can also shut off power to the entire house. Tape a note on the main electrical panel to warn others not to reactivate it.
Consult local electrical codes in your area to be sure you are installing the wiring safely and consistently with those requirements.
Have an electrician handle the electrical part of installing a garbage disposal if you are not knowledgeable about local code requirements or basic electrical wiring, specifically if adding a GFCI outlet and corresponding switch.
Step 7: Test the Unit
Turn on power to the circuit you’re using to power the disposal and turn the water back on. Activate the device, while running cold water down the drain. If the garbage disposal does not fire up, re-check the connections. Let the water run for a few minutes and check for any leaks from the pipe connections under the sink.
Great job! Now you’ll wonder why you hadn’t installed a disposal sooner.