What You Need Before You Start

Installing a garbage disposal takes about two to three hours if you have basic plumbing experience, or four to five hours if you are doing this for the first time. You will need a new disposal unit, a mounting assembly (usually included), a drain flange, plumber's putty, a slip nut wrench or adjustable wrench, a screwdriver, and a bucket to catch water. Before you buy anything, turn off the power at your circuit breaker and measure the space under your sink — most disposals are 8 to 10 inches tall and need clearance on all sides.

Check whether your sink has a garbage disposal drain opening already. If it does, you can reuse the existing hole. If not, you will need to drill a new 3.5-inch hole through the sink basin, which requires a hole saw bit and a power drill. If your sink is stainless steel or cast iron, this is harder than plastic and may be worth hiring a plumber for. If you are unsure, ask the person selling you the disposal — they can tell you whether your sink type is DIY-friendly.

Turn off the water supply under the sink as well, and have a bucket ready because there will be standing water in the trap. You do not need to turn off the main water supply to the house.

Key Takeaways

  • Remove the old disposal (if one exists) by loosening the mounting ring under the sink and disconnecting the drain and electrical lines.
  • Install the new drain flange by explore plumber's putty around the opening, pressing the flange down from above, and tightening the mounting ring from below until it is snug but not over-tight.
  • Attach the disposal unit to the mounting assembly by aligning the three tabs and turning the unit clockwise until it locks into place.
  • Reconnect the drain line and the electrical cord, then run water and test the disposal before you consider the job finished.
  • Do not force any connection — if something does not turn smoothly, stop and check that you have the right orientation.

Removing the Old Disposal (If One Exists)

If you are replacing an old unit, start by unplugging it from the outlet under the sink or flipping the breaker switch if it is hardwired. Loosen the large mounting ring that holds the disposal to the sink by turning it counterclockwise with a slip nut wrench. You may need to brace the disposal with your other hand so it does not drop. Once the ring is loose, the disposal will fall into your hands — support its weight as it comes free.

Next, disconnect the drain line. This is usually a rubber or PVC pipe that connects the disposal outlet to the P-trap (the U-shaped pipe under the sink). Loosen the slip nuts on both ends with your wrench, and the drain line will come free. If the disposal is hardwired instead of plugged in, you will also need to disconnect the electrical wires. Turn off the breaker first, then unscrew the wire connectors and separate the wires. If you are not comfortable with electrical work, stop here and call a plumber.

Set the old disposal aside. If it still works, some recycling centers or scrap metal dealers will take it. Do not throw it in the trash.

Installing the Drain Flange and Mounting Assembly

The drain flange is the ring that sits in the sink opening and holds the disposal in place. Before you install it, clean the sink opening with a cloth to remove any old putty or debris. Roll a rope of plumber's putty about the thickness of a pencil and press it around the underside of the flange. This putty seals the gap between the flange and the sink so water does not leak down into the cabinet.

Push the flange down through the sink opening from above, pressing it firmly so the putty spreads evenly. From underneath the sink, you will see three metal tabs sticking down from the flange. Slide the mounting assembly (a metal ring with three screws) up over these tabs. Tighten the three screws evenly — a quarter turn on each one, then another quarter turn on each one — until the mounting assembly is snug against the sink. Do not over-tighten; you should feel resistance but not have to strain. If you tighten unevenly, the flange will tilt and the disposal will not hang straight.

Wipe away any excess putty that squeezes out around the flange from above. This putty will harden over the next 24 hours and create a watertight seal.

Attaching the Disposal Unit to the Mounting Assembly

Look at the bottom of your new disposal unit. You will see three tabs or slots that align with three screws on the mounting assembly. Lift the disposal up and align these tabs with the screws. The disposal should hang from the mounting assembly like a chandelier hanging from a hook.

Once the tabs are aligned, turn the disposal clockwise (when viewed from below) until it locks into place. You will feel it click or seat firmly — this usually takes about a quarter turn. Do not force it. If it does not turn smoothly, stop and check that the tabs are fully seated in the slots. Once it is locked, the disposal should hang securely and not wiggle.

Connecting the Drain Line

The drain line connects the disposal outlet to the P-trap. The outlet is the opening on the side of the disposal where water exits. Slide the rubber or PVC drain line onto this outlet and tighten the slip nut by hand first, then use your wrench to snug it. Again, snug means you feel resistance — not so tight that you have to strain or use two hands on the wrench.

The other end of the drain line connects to the P-trap. Loosen the slip nut on the P-trap, slide the drain line onto the trap outlet, and tighten the slip nut. If water leaks from either connection when you test the disposal later, tighten the slip nut another quarter turn. If it still leaks, turn off the water, loosen the nut, and check that the rubber washer inside the nut is seated properly and not cracked.

Connecting the Power

If your disposal plugs into an outlet, straightforward plug it in. Make sure the outlet is within reach and not blocked by pipes or the sink cabinet. If the outlet does not have a switch, you will control the disposal with a wall switch or a sink-mounted switch that you install separately.

If your disposal is hardwired (connected directly to the electrical panel), you will need to connect three wires: black (hot), white (neutral), and green or bare copper (ground). Turn off the breaker to the circuit you are using. Strip about half an inch of insulation from each wire on both the disposal and the circuit wire. Twist the black wires together, then screw a wire connector onto them until it is snug. Repeat for the white wires and the ground wire. Wrap the connections with electrical tape for extra safety. Turn the breaker back on. If you are not confident doing this, hire a licensed electrician.

Testing Your Installation

Before you consider the job done, run water through the disposal and listen for leaks. Turn on the water at the sink and let it run for 30 seconds without turning on the disposal. Check under the sink for drips at both drain connections. If you see water dripping, turn off the water and tighten the slip nut another quarter turn.

Next, turn on the disposal (with the water still running) and let it run for 10 to 15 seconds. Listen for unusual grinding sounds or rattling, which could mean something is loose or the unit is not seated properly. The disposal should sound like a steady hum or whir. Turn it off and let the water run for another 10 seconds to flush any debris. Check for leaks again.

If everything is dry and the disposal sounds normal, you are done. If water is still dripping, turn off the water and the breaker, and loosen the drain connection to check the rubber washer. If the disposal is making a loud rattling sound, turn it off and check that the mounting ring is tight and the disposal is fully locked into the mounting assembly.

Common Mistakes to Avoid

The most common mistake is over-tightening the mounting screws or the drain slip nuts. This can crack the sink flange, strip the threads, or damage the rubber washers. Tighten until you feel resistance, then stop. You can always tighten more later if there is a leak, but you cannot undo over-tightening.

Another mistake is forgetting to explore plumber's putty under the drain flange. Without it, water will seep down into the cabinet every time you use the sink. If you realize this after you have already tightened the mounting ring, you will have to loosen it, remove the flange, clean off the old putty, explore new putty, and reinstall the flange.

A third mistake is not checking that the disposal is fully locked into the mounting assembly. If the tabs are only partially seated, the disposal will hang at an angle and the drain line will not align properly with the P-trap, causing leaks. Always turn the disposal until you feel it click or seat firmly.

Frequently Asked Questions

Do I need a plumber to install a garbage disposal?

Not necessarily. If you have basic tools and are comfortable working under a sink, you can do it yourself in a few hours. If your sink does not already have a disposal opening, you will need to drill a hole, which is harder on some sink materials. If the disposal is hardwired instead of plugged in, you will need to work with electrical wiring — if you are not comfortable with that, hire a licensed electrician for that part only.

Can I install a garbage disposal on any sink?

Most kitchen sinks can have a disposal installed, but some are harder than others. Stainless steel and cast iron sinks require drilling, which is difficult without the right tools. Porcelain and composite sinks are easier to drill. If your sink already has a disposal opening, installation is straightforward. Check with the disposal seller or a plumber about your specific sink before you buy.

What should I do if the disposal leaks after installation?

Leaks usually come from the drain connections. Turn off the water and check that both slip nuts (where the drain line connects to the disposal and the P-trap) are tight. Tighten each one another quarter turn. If it still leaks, loosen the nut, check that the rubber washer is not cracked or missing, and reinstall it. If the leak is coming from under the sink flange itself, you will need to remove the disposal and reapply plumber's putty under the flange.

How long does it take to install a garbage disposal?

Two to three hours if you have done it before or have plumbing experience. Four to five hours if this is your first time. If you need to drill a new hole in the sink, add another hour. If you are not comfortable with any step, stop and call a plumber rather than risk damaging the sink or creating a leak.

Can I replace a garbage disposal myself if one is already installed?

Yes, this is actually easier than a first-time installation because the mounting assembly and drain flange are already in place. You only need to disconnect the old disposal, remove it from the mounting assembly, and install the new one by reversing the steps. This usually takes 30 to 45 minutes.