How to Install a Garbage Disposal
Updated February 20, 2026
Install or replace a garbage disposal from start to finish -- remove the old unit, mount the new one, wire the electrical, and connect the drain plumbing without leaks.
Overview
Replacing a garbage disposal is a 1-2 hour job that most homeowners can handle. If you are swapping an existing unit, it is even easier -- the outlet, mounting hardware, and drain plumbing are already there. Brand-new installations are more involved because you may need an electrical outlet added and drain plumbing modified, but still doable for a confident DIYer. One thing to know upfront: InSinkErator and Waste King use different mounting systems that are not interchangeable. Staying with the same brand when replacing is the path of least resistance.
What You'll Need
Safety First
- Kill the breaker before you touch anything. Verify with a non-contact voltage tester that the outlet or wiring under the sink is dead. Electrical shock in a wet environment is no joke.
- Need a new electrical circuit for a first-time installation? Hire a licensed electrician. Running a new circuit involves codes, wire sizing, GFCI requirements, and working inside the breaker panel -- not DIY territory.
- These units are heavy (8-15 pounds). You will be holding it overhead with one hand while turning the mounting ring with the other. Get a helper, or put a bucket under it to support the weight during mounting.
- On a septic system? Make sure the disposal is septic-rated. Some municipalities ban disposals on septic entirely -- check your local codes first.
Step-by-Step Instructions
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Remove the Old Disposal (If Replacing)
Breaker off. Unplug the disposal (or disconnect hardwired connections after verifying power is dead). Bucket under the P-trap. Loosen the slip-joint nut to disconnect the discharge pipe. Disconnect the dishwasher drain hose if there is one. Support the disposal with one hand and turn the lower mounting ring counterclockwise to release it -- the unit drops free and it is heavy, so be ready. Same brand replacement? The existing mounting assembly stays. Switching brands? You will need to remove the old mount and install the new one.
Tip: Take photos of the discharge pipe, dishwasher hose, and electrical connections before removing anything. Gives you a clear reference when hooking up the new unit, especially if the routing is not obvious. -
Install the Sink Flange and Mounting Assembly
New installation or switching brands? You need to install the mounting assembly. Remove the old sink strainer (loosen the locknut from below). Clean the sink opening. Roll a rope of plumber's putty around the underside of the new sink flange, drop it into the opening from above, and press firmly. From below, slide on the fiber gasket, backup flange, and mounting ring. Tighten the three mounting screws evenly until the flange seats against the sink and putty squeezes out around the edges. Wipe excess from above.
Warning: Tighten the three screws evenly -- quarter-turn passes in rotation. Do not tighten one fully before the others. Uneven tightening cocks the flange and creates a leak. -
Wire the Electrical Connection
Plug-in style with an existing outlet? Remove the electrical cover plate on the bottom of the disposal. Feed the power cord through the strain relief. Wire it up: black to black (hot), white to white (neutral), green to the green ground screw. Wire nut each connection and tug-test to confirm they are tight. Tuck the wires in, replace the cover plate, and plug in. Hardwired installations are the same process but with house wiring instead of a cord.
Warning: Breaker must be OFF and verified with a voltage tester before any electrical work. Double-check every wire nut connection -- a loose one can arc and start a fire inside the housing. The ground wire goes to the green screw, no exceptions. -
Mount the Disposal to the Sink Flange
Have a dishwasher? Knock out the dishwasher inlet plug before mounting -- use a screwdriver and hammer to push it into the chamber, then fish it out with pliers. No dishwasher? Leave the knockout in place. Lift the disposal up, align the mounting tabs with the ring on the sink flange, and turn the lower ring clockwise until it locks. The unit should hang solid with no wobble.
Tip: Working alone? Set a bucket or sturdy box under the disposal to support it while you turn the mounting ring. Holding 10+ pounds overhead with one hand while twisting with the other is miserable without support. -
Connect the Drain Plumbing
Attach the discharge tube to the disposal outlet with the gasket and flange provided, bolts tightened evenly. Connect the tube to the P-trap with a slip-joint connection. If the trap does not line up (common when the new unit is a different size), you need a tailpiece extension or offset fitting. Dishwasher? Connect the drain hose to the disposal inlet with a hose clamp. Make sure the hose has a high loop -- it should rise to countertop level before coming back down to the disposal.
Tip: The high loop on the dishwasher hose is not optional. Without it, dirty disposal water back-siphons into the dishwasher. Some codes require an air gap fitting instead of a high loop -- check your local requirements. -
Test for Leaks and Verify Operation
Breaker back on. Fill the sink with 2-3 inches of water and release it all at once. While it drains, check every connection: sink flange putty seal, discharge tube, P-trap slip joints, dishwasher hose clamp. Tighten anything that drips. Once leak-free, run cold water and flip the disposal on. It should spin freely and drain quickly. Drop a few ice cubes in to test grinding. One more check under the sink during operation. Done.
Tip: Ice cubes for the first run -- they clean the grinding surfaces and confirm the impeller spins freely. If you hear excessive vibration or rattling, the disposal may not be seated level on the mounting ring. Turn it off and reseat it.
Pro Tips
- Same brand replacement? The mounting assembly stays on the sink and you just swap the unit. Cuts installation time in half.
- Get at least 1/2 HP for one person, 3/4 HP or more for a family. The 1/3 HP models jam constantly and struggle with anything harder than lettuce. The price difference between 1/2 and 3/4 HP is usually only $30-50.
- Continuous-feed (wall switch) disposals are cheapest and most common. Batch-feed (activated by a stopper, no switch needed) are safer with young kids but cost more.
- Mounting ring hard to turn? A little plumber's grease on the tabs makes it lock in easier and makes future removal smoother too.
- Save the Allen wrench that comes with the disposal. Zip-tie it to the unit for quick access when you need to unjam it later -- because you will.
When to Call a Pro
Call a pro if you need a new electrical circuit (licensed electrician territory), if the sink opening needs to be modified, if the drain plumbing needs major reconfiguration, if you are on septic and want to confirm compatibility, or if the old mounting assembly is corroded solid and will not come off without damaging the sink.