What you need to know before you start

Installing a garbage disposal is a job you can do yourself if you have basic plumbing experience and the right tools, but it involves working with electrical wiring and plumbing connections that can go wrong. If you are not comfortable working with either, or if your sink is already leaking, call a plumber — the cost of a professional installation (usually $150 to $300) is less than the cost of fixing water damage or an electrical problem.

Before you buy a disposal, check whether your sink has a knockout plug — a removable disc in the drain opening. If it does not, you have a disposal-ready sink. If your sink drains to a septic system rather than a municipal sewer, check your septic tank manual first; some systems do not handle disposals well.

You will also need to know whether you have a hardwired disposal (connected directly to your home's electrical system) or a plug-in disposal (connected to an outlet under the sink). Plug-in models are simpler to install if an outlet is already there. Hardwired models require running electrical wire, which you should leave to a licensed electrician.

Key Takeaways

  • A plug-in garbage disposal is easier to install than a hardwired one and requires only basic plumbing connections and an existing outlet under the sink.
  • You will need a mounting ring, rubber gasket, and sink flange that come with the disposal, plus a wrench, screwdriver, and plumber's putty.
  • The disposal connects to your drain tailpiece with a slip nut and rubber washer, and you must turn off the electrical outlet before you begin work.
  • If your sink does not have a knockout plug, you cannot install a disposal without replacing the entire sink strainer assembly.
  • Water leaks at the sink flange or drain connection are the most common problem after installation and usually mean the rubber gasket needs to be reseated or replaced.

Gather your tools and materials

You will need the disposal unit itself, which comes with a mounting ring, rubber gasket, and sink flange. You will also need plumber's putty (a clay-like sealant), a wrench or adjustable wrench, a screwdriver, and a bucket to catch water from the old drain. Have a flashlight ready so you can see under the sink clearly.

If you are replacing an old disposal, you may also need a slip nut wrench or a pipe wrench to loosen the connection between the old unit and the drain line. A regular wrench works in most cases, but a slip nut wrench grips the nut without slipping as easily.

Before you start, turn off the electrical outlet under the sink at the wall switch or breaker box. If there is no outlet, or if the disposal is hardwired, stop here and call an electrician.

Remove the old disposal and prepare the sink opening

If you are replacing an existing disposal, unplug it from the outlet first. Use your wrench to loosen the slip nut that connects the disposal to the drain line — this is the large nut where the disposal meets the pipe coming from the wall. Turn it counterclockwise by hand or with the wrench until it comes free. Water may spill, so have your bucket ready.

Next, loosen the three bolts that hold the mounting ring to the sink flange. These bolts are on the underside of the sink, inside the mounting ring. Turn them counterclockwise with a screwdriver until they are loose enough to lift the old disposal away. Set it aside.

Once the old disposal is out, scrape away any old plumber's putty from the sink opening with a screwdriver or putty knife. Wipe the opening clean with a damp cloth and dry it completely. This is also the time to remove the old rubber gasket and inspect the sink flange for cracks or damage. If the flange is cracked, you will need to replace the entire sink strainer assembly, which requires removing the sink itself — call a plumber for this job.

Install the new mounting ring and gasket

Take the new rubber gasket that came with your disposal and slide it over the sink flange from underneath. The gasket should sit flat against the underside of the sink. If it does not fit smoothly, check that you have the right size disposal for your sink opening.

Next, slide the mounting ring up over the sink flange from underneath. The three bolts on the mounting ring should align with three holes or slots in the sink flange. Hand-tighten all three bolts first, then use your screwdriver to tighten them in a crisscross pattern — tighten one bolt, then the one across from it, then the third one. This keeps the gasket seated evenly. Tighten until the mounting ring is snug against the sink, but do not over-tighten, which can crack the sink.

From the top of the sink, explore a ring of plumber's putty around the sink opening, just inside the drain rim. This creates a watertight seal. Press it firmly into place with your finger.

Connect the disposal to the mounting ring

Lift the new disposal up under the sink and align the three mounting lugs on the disposal with the three bolts on the mounting ring. The disposal should slide up and lock into place. You will hear or feel a click when it is seated correctly.

Once the disposal is locked in, tighten the three bolts on the mounting ring by turning them clockwise with a screwdriver. Tighten them evenly, just as you did when you installed the mounting ring. The disposal should be held firmly in place and should not wiggle or rotate.

Wipe away any excess plumber's putty from around the sink opening with a damp cloth. This putty will harden over the next few hours and create a permanent seal.

Connect the drain line and test for leaks

The drain line from the wall (or from the P-trap under the sink) connects to the disposal with a slip nut and rubber washer. Slide the rubber washer onto the drain line first, then slide the slip nut over it. Hand-tighten the slip nut onto the threaded outlet on the disposal, then use your wrench to tighten it another quarter turn. Do not over-tighten; the rubber washer does the sealing, not the nut.

Before you plug in the disposal, turn on the water and let it run for 30 seconds while you watch underneath the sink. Check for drips at the sink flange, at the slip nut connection, and at any other joints. Small drips that stop after a few seconds are normal as the gasket settles. Steady drips mean you need to tighten the connection or reseat the gasket.

If water is leaking from the sink flange itself, turn off the water and tighten the three bolts on the mounting ring a bit more. If water is leaking from the slip nut, tighten that nut another quarter turn with your wrench. Let the water run again and check.

Plug in the disposal and run a test cycle

Once you have confirmed there are no leaks, plug the disposal into the outlet under the sink. Do not turn it on yet. Fill the sink halfway with cold water, then turn on the disposal and let the water drain. Listen for any unusual grinding or rattling sounds, which could mean something is stuck inside or the unit is not mounted securely.

Run the disposal for about 10 seconds, then turn it off and let the water drain completely. Repeat this two or three times. The disposal should be quiet and should drain smoothly. If you hear grinding or the water drains slowly, turn off the disposal when ready and check that nothing is blocking the drain line.

After the test cycle, run cold water through the disposal for another 10 seconds to flush out any debris. Do not put food waste down the disposal for at least 24 hours, to allow the plumber's putty to harden completely.

Frequently Asked Questions

Can I install a garbage disposal if I do not have an outlet under the sink?

No, not without hiring an electrician to install one. A plug-in disposal needs a dedicated outlet within reach of the power cord. If you do not have an outlet, you have two options: hire an electrician to run a new circuit and outlet, or buy a hardwired disposal and have an electrician wire it directly to your home's electrical panel. Both cost more than a plug-in installation.

What should I do if water leaks from under the sink after installation?

First, identify where the leak is coming from. If it is at the sink flange (where the disposal meets the sink), tighten the three bolts on the mounting ring a quarter turn at a time until the leak stops. If it is at the slip nut where the drain line connects, tighten that nut a quarter turn. If the leak continues, turn off the water and tighten the mounting ring bolts more firmly, or remove the disposal and reseat the rubber gasket.

Can I install a disposal on a double sink?

Yes, but only on one side. The disposal connects to whichever sink basin has the drain opening with the knockout plug. The other side drains normally through a separate tailpiece. If both sides have knockout plugs, you can choose which one to use, but you can only install one disposal per sink.

Do I need to use plumber's putty, or can I use caulk instead?

Plumber's putty is the correct material because it stays pliable and does not harden like caulk does. If you use caulk, it will crack when the sink flexes or when you tighten the mounting bolts. Plumber's putty is inexpensive and available at any hardware store.

What if the disposal does not lock onto the mounting ring?

The three mounting lugs on the disposal may not be aligned with the bolts on the mounting ring. Rotate the disposal slightly until you feel the lugs drop into place, then push up firmly. You should hear a click. If the disposal still will not lock, check that the mounting ring is installed correctly and that the bolts are not over-tightened.