What you need to know before you start

Installing a garbage disposal means connecting it to the drain under your sink and wiring it to a switch or outlet. The job involves three separate tasks: removing the old drain (if there is one), mounting the disposal unit itself, and running the electrical connection. Most homeowners can handle the plumbing part with basic tools. The electrical part is where you need to decide whether to call a licensed electrician—it depends on your local code and your comfort level with wiring.

The disposal sits in the cabinet below your sink and connects to the drain pipe that leaves your sink basin. Water and food waste flow down through the disposal, get ground up, and exit through the drain line to your septic system or municipal sewer. The whole assembly takes two to four hours if you are doing it yourself, or one to two hours if an electrician is handling both plumbing and wiring.

Key Takeaways

  • You will need a screwdriver, adjustable wrench, plumber's putty, and a bucket to catch water from the old drain before you disconnect anything.
  • The disposal mounts to a ring under the sink basin using a series of tabs and a locking collar that you turn by hand or with a wrench.
  • The drain line from the disposal connects to the existing P-trap using a slip nut, which you can tighten by hand and then snug with a wrench.
  • Electrical connection requires either a hardwired setup (which needs a licensed electrician in most places) or a plug-in cord to a nearby outlet, depending on your local code.
  • Before you turn on the disposal for the first time, run cold water for several seconds to flush the system and check for leaks.

Gather your tools and materials

You will need a screwdriver (both Phillips and flathead), an adjustable wrench, a bucket, plumber's putty, and a flashlight. Have towels nearby because water will spill when you disconnect the old drain. If your sink has a garbage disposal already, you may be replacing it; if not, you are installing one for the first time.

The disposal unit itself comes with a mounting ring, a locking collar, and usually a dishwasher inlet (a small port on the side). Your local code may require a disconnect switch within sight of the disposal, or it may allow a plug-in cord under the sink. Check your local electrical code or ask your electrician before you buy the disposal, because some models come hardwired and others come with a cord.

Remove the old drain and clean the sink opening

Turn off the water and place a bucket under the P-trap (the curved pipe below the sink). Loosen the slip nuts on both sides of the P-trap with your wrench and remove the trap. If there is an old disposal, disconnect it from the drain line and remove the mounting collar by turning it counterclockwise (usually by hand, sometimes with a wrench). If there is just a drain basket, unscrew the locknut underneath and pull the basket out from above.

Clean the sink opening thoroughly. Scrape away old putty and debris with a flathead screwdriver. Dry the rim completely. This is where the new mounting ring will sit, and it needs to be clean so the putty seals properly and the ring sits flush.

Install the mounting ring and disposal unit

Roll a rope of plumber's putty about the thickness of a pencil and press it around the underside of the mounting ring. Push the ring up through the sink opening from below so the putty creates a watertight seal. From above, you will see the ring sitting flush in the drain hole.

Slide the disposal unit up under the sink and align the three mounting tabs on the disposal with the three slots in the mounting ring. Turn the locking collar clockwise (by hand or with a wrench, depending on the model) until the disposal is tight against the ring. The disposal should not move or rattle. Wipe away any excess putty from above the sink with a damp cloth.

Connect the drain line and P-trap

The drain outlet on the disposal is a threaded port. Slide the slip nut from your new drain line onto this port and hand-tighten it first. You should be able to turn it with your fingers until it is snug. Then use your wrench to turn it one more quarter turn—do not over-tighten, because you may crack the fitting.

Reconnect the P-trap to the drain line coming from the disposal. Hand-tighten both slip nuts, then snug each one with a wrench. Place your bucket underneath and run water into the sink for 10 seconds. Check both connections for drips. A small weep is normal while the putty is still soft, but a steady drip means the nut needs another quarter turn.

Handle the electrical connection

This is where you need to know your local code. Some jurisdictions require a licensed electrician for any hardwired appliance. Others allow a homeowner to plug the disposal into a standard outlet under the sink, as long as that outlet is on a dedicated 15-amp circuit with a ground fault circuit interrupter (GFCI) breaker.

If you are plugging it in, make sure the outlet is within reach of the disposal's cord and that the cord does not run through standing water. If you are hardwiring it, you will need to run a wire from your electrical panel to a disconnect switch near the disposal, then from the switch to the disposal itself. This requires turning off the main breaker and working inside the panel—call a licensed electrician for this step.

Do not turn on the disposal until the electrical connection is complete and you have checked for leaks in the plumbing.

Test the disposal and check for leaks

Turn on the water and let it run for 10 seconds before you flip the disposal switch. This fills the chamber and clears any air. Then turn on the disposal and let it run for 30 seconds while water flows. Listen for grinding sounds and watch underneath for leaks. Turn off the disposal and let the water run for another 10 seconds to flush out any remaining debris.

Check both the mounting ring seal and the P-trap connections. If you see water dripping, turn off the disposal and tighten the slip nuts another quarter turn. If putty is still oozing out around the mounting ring, that is normal—it will harden over the next few hours. Do not run the disposal again until any leaks have stopped.

When to call a professional

Call a licensed plumber if the disposal does not sit flush against the mounting ring, if you cannot get the P-trap connections to stop leaking after tightening, or if the drain line does not fit your existing pipes. Call a licensed electrician if your local code requires hardwiring, if you are not comfortable working inside your electrical panel, or if there is no outlet under the sink and you do not want to install one.

If the disposal is grinding but water is backing up into the sink, the problem is downstream in the main drain line, not the disposal itself—that is a separate issue that a plumber will need to diagnose.

Frequently Asked Questions

Do I need a plumber to install a garbage disposal?

The plumbing part is straightforward enough for most homeowners with basic tools. The electrical part is where you may need a professional—check your local code first. If you are uncomfortable working under the sink or your pipes do not match the standard setup, a plumber can finish the job in an hour or two.

Can I install a disposal if my sink does not have a drain hole?

No. A disposal requires a standard sink drain opening. If your sink has no drain or a non-standard opening, you would need to have a new hole drilled by a professional, which is expensive and risky depending on the sink material.

What size circuit breaker do I need for a garbage disposal?

Most disposals run on a 15-amp circuit, though some larger models need 20 amps. Check the specifications on your disposal before you wire it. The circuit should be dedicated to the disposal only—do not share it with other appliances.

Can I connect the dishwasher drain to the garbage disposal?

Yes. The disposal has a small inlet port on the side for this purpose. You will need a hose clamp and a rubber hose to connect the dishwasher drain line to this port. Some disposals come with a knockout plug in this port that you remove first.

What should I do if the disposal leaks from the bottom?

A leak from the bottom usually means the internal seal has failed and the unit needs to be replaced. Turn off the power, disconnect it, and install a new one using the same mounting ring and drain line. This is not a repair—disposals do not have user-serviceable seals.