What are expert tips for replacing an existing garbage disposal?

If upgrading from 1/3 HP to 3/4 HP or larger, check that drain piping can handle the bigger unit's discharge. Always knock out the dishwasher drain plug before mounting -- if you forget, dishwasher water backs up onto your counter. Save the disposal wrench and tape it to the inside of the cabinet door for when the unit jams.

What mistakes should I avoid with replacing an existing garbage disposal?

Not turning off the breaker -- the wall switch isn't enough. Forgetting the dishwasher drain plug -- single most common disposal installation mistake. Not enough plumber's putty under the sink flange. Overtightening the discharge pipe connection.

Replacing an Existing Garbage Disposal

Installation Guide Easy to Intermediate 30-60 minutes $0 labor DIY / $100-$200 with plumber

Created by Ryan Pietrzak Illinois Licensed Plumber · In the plumbing industry since 2009

Updated February 20, 2026

Key Takeaway

Replacing a garbage disposal is one of the fastest plumbing upgrades you can do. If the new unit uses the same mounting system as the old one, you can have it swapped in 30 minutes. Even with a different mount, it's still under an hour. The electrical connection is just three wires in a junction box -- nothing complicated.

Overview

What to Know

Matching the Mount System

Most disposals use the EZ Mount (InSinkErator and many others) or the 3-Bolt mount (Waste King and some others). If your new unit matches the old mount, reuse the existing mounting ring and sink flange -- just twist the new unit on. Different mount type? Remove the old flange and install the new one, adds about 20 minutes.

Electrical Connection

Disposals are either hardwired (wires from the wall) or cord-connected (plugs into an outlet). If the old one was hardwired, the new one probably will be too. Upgrading from corded to hardwired requires a wall switch -- that's where an electrician comes in.

Tools & Materials

Screwdriver (flathead and Phillips)
Adjustable wrench or pliers
Plumber's putty
Wire nuts (usually included)
Bucket and towels
Disposal wrench (usually included)

Step by Step

Disconnect power
Flip the circuit breaker for the disposal. Verify it's off by flipping the wall switch. If plugged in, unplug it. Never work on the electrical connection with power on.
Remove the old disposal
Bucket underneath. Disconnect the discharge pipe. Disconnect dishwasher drain hose if present. Support the unit with one hand, rotate the mounting ring counterclockwise. It drops right off.
Disconnect the wiring
Remove the cover plate on the bottom of the old unit. Disconnect wire nuts on black, white, and green wires. Set old unit aside.
Wire the new disposal
Remove cover plate on new unit. Feed house wires through cable clamp. Black to black, white to white, green to green screw. Secure with wire nuts, replace cover plate.
Mount the new disposal
If mounts match, lift new unit and rotate mounting ring clockwise until it locks. If changing mount types, install new sink flange first (plumber's putty, tighten from below), then mount the unit.
Reconnect plumbing and test
Reconnect discharge pipe. If you have a dishwasher, knock out the drain plug inside the disposal inlet and reconnect the hose. Turn on power, run water, test.

Pro Tips

If upgrading from 1/3 HP to 3/4 HP or larger, check that drain piping can handle the bigger unit's discharge.
Always knock out the dishwasher drain plug before mounting -- if you forget, dishwasher water backs up onto your counter.
Save the disposal wrench and tape it to the inside of the cabinet door for when the unit jams.

Mistakes to Avoid

Not turning off the breaker -- the wall switch isn't enough.
Forgetting the dishwasher drain plug -- single most common disposal installation mistake.
Not enough plumber's putty under the sink flange.
Overtightening the discharge pipe connection.

When to Call a Pro

If you need a new electrical circuit or wall switch, call an electrician. If the drain needs reconfiguring (adding dishwasher connection, changing pipe sizes), a plumber handles that. The disposal swap itself is DIY territory.

Bottom Line

A disposal replacement is a 30-60 minute job with basic tools, saving $100-$200 in labor. Match the mount type to make it faster, and don't forget that dishwasher drain plug.