Garbage disposal installation: what to know

What the job involves, what changes the price, and what to ask a pro.

What garbage disposal installation is

Garbage disposal installation mounts a new disposal under the kitchen sink, connects it to the drain and the dishwasher inlet if there is one, and wires it to a switch or outlet. It is a common upgrade when the old unit is failing or when a sink has no disposal at all.

Signs you need it

  • The current disposal is past its service life, hums without spinning, or leaks from the body
  • You want a disposal in a sink that has no mounting or drain set for one
  • The old disposal is the wrong size or mounting type for the sink's drain flange
  • The dishwasher drains into the disposal, and the connection is leaking or missing
  • The disposal switch is loose, damaged, or has no working outlet nearby

What the pro does

  • Check the sink drain flange and the mounting ring, and confirm the disposal's mount type and the outlet or switch wiring
  • Turn off the power at the breaker, then remove the old unit and disconnect the drain and dishwasher lines
  • Mount the new disposal with the mounting ring, gaskets and mounting screws, and set the body square under the sink
  • Connect the drain flange and the discharge pipe, then knock out the dishwasher plug and attach the dishwasher hose if there is a dishwasher, or leave the plug in if there is not
  • Wire the disposal to the switch or the cord with the correct cable, and make the connection in the junction box or outlet
  • Restore power, run water through the disposal, and check every joint and the mount for leaks and vibration

What changes the price

Every job is different, so we do not publish prices. These are the things that move the quote up or down.

  • Mount type and whether the sink flange and drain pipe need changes to match
  • Whether the dishwasher connection must be added or moved
  • Electrical work: an existing outlet under the sink or a new switch and circuit
  • Condition of the drain pipe and trap, and whether they must be replaced
  • Access under the sink and whether the cabinet or plumbing must be moved
  • Disposal model and whether the unit has a special feature such as a sound shield or a septic-safe rating

What a written quote should spell out

  • Disposal model and horsepower, and the mounting type
  • Drain flange, trap and discharge pipe, new or reused
  • Dishwasher connection, if one is present, and whether the knockout plug is removed and the hose connected
  • Electrical hookup: the outlet or switch used and who makes the connection
  • Whether the old unit is removed and disposed of

Questions to ask before you hire

  • Does the new disposal match my sink's mounting type, and will the drain line fit?
  • Will you connect the dishwasher drain, and do you add an air gap or high loop?
  • Is there a switch or outlet under the sink for the disposal?
  • Who makes the electrical connection, and is it covered by the install?
  • Will you test the drain and the mount for leaks and vibration before you leave?
  • Do you check the drain pipe and trap for corrosion when the disposal is installed?

Red flags

  • Pro who wires the disposal without turning the power off at the breaker first
  • Pro who connects the dishwasher drain without an air gap or a high loop, where the local rules require one
  • Pro who leaves the mount loose or over-tightened, which causes leaks and cracked bodies
  • Pro who runs a disposal without a test run under water

What you can do yourself

A homeowner can install a disposal on a simple setup if the power is off at the breaker and the outlet or switch is already wired. Call a pro if the dishwasher drain or the electrical hookup must change, since a wrong dishwasher connection can flood the kitchen and a wrong electrical hookup can shock or start a fire.

Licenses and permits

Disposal installation's plumbing portion is commonly licensed plumbing work, and the electrical hookup may need a licensed electrician in some areas. Check with your state or local licensing agency about what applies to the plumbing and electrical work.

Garbage disposal installation questions

Do I need a switch for a garbage disposal?

Many disposals need a switch, a cord, or a wall outlet with a switch. The pro should confirm what is already in place and what the new unit requires before the install.

Why does a dishwasher connection need an air gap or a high loop?

They stop dirty water from flowing back into the dishwasher when the drain backs up. Where the local rules require an air gap, it must be installed. The pro should check the rule before connecting the line.

What size disposal should I get?

The right size depends on how the kitchen is used and the mount type of your sink. The pro should check the mount first, then match the motor to your use.

Why does my new disposal leak at the mount?

A loose mounting ring, a gasket that is not seated, or a mounting screw that is over-tightened are the usual causes. The pro should set the mount and test it with water.

About this guide

This national guide is written and checked by infinibell. Rules and conditions differ by place, so local pros are credited on guides for the cities they serve, not on national ones.

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