Installing a new garbage disposal is a job many homeowners can do in a couple of hours, and a few details make the difference between a unit that lasts and one that leaks in a month. This guide covers what you need, the steps in order and the points where a plumber is worth calling.
Whether you are replacing an old unit or adding one under a sink that never had it, start by turning off power at the breaker, not just the wall switch.
What you need before you start
- A disposal that fits your sink and a mounting kit that matches it.
- Plumber's putty or the gasket supplied for the flange.
- A power cord kit or access to a hardwired connection and an outlet switch.
- A bucket, rags, a screwdriver, a hex key and channel lock pliers.
- A flashlight and a way to keep the dishwasher drain hose out of the way.
Step by step
- 1
Cut power and disconnect
Switch off the breaker, confirm it is dead, then disconnect the old unit and the drain pipe.
- 2
Remove the old mount
Loosen the mounting ring, lift the unit away and remove the old sink flange.
- 3
Seat the new flange
Press putty under the new flange, set it in the drain opening and tighten the mount from below.
- 4
Hang and wire the unit
Lift the disposal onto the mount, connect the wiring and attach the drain outlet and trap.
Last, reconnect the dishwasher hose. On a new disposal the dishwasher inlet has a plastic knockout that must be removed with a hammer and screwdriver before the hose goes on. Skipping that step leaves the dishwasher unable to drain.
Run water, then test the unit for leaks at the flange, the drain joint and the dishwasher connection before you close the cabinet.
Where a plumber earns the call
| Situation | Why it matters | Best approach |
|---|---|---|
| Old flange corroded or cracked | A new unit will not seal on a bad flange | Replace the flange or call a plumber |
| No outlet under the sink | Electrical work may be needed | Hire a licensed electrician or plumber |
| Existing trap or drain misaligned | Leaks and slow drains follow | A plumber fixes the pipe alignment |
| No existing disposal | Adds electrical and drain changes | Plan with a plumber |
Our garbage disposal repair page explains when we repair a unit and when we replace it, and we install customer supplied disposals too.
Avoiding the common mistakes
Forgetting the dishwasher knockout is the most frequent error. Overtightening the mounting ring and cracking the sink flange is the second. Using too much putty and squeezing it into the drain is a third, because it later breaks loose and clogs.
Choose a unit with enough power for your kitchen. A larger household that cooks daily will be better served by a stronger motor than a minimal one, and a cheap unit often jams more.
Choosing the right disposal
Disposals come in continuous feed and batch feed styles. Continuous feed runs while a switch is on and suits most kitchens. Batch feed only runs with the stopper in place, which some households prefer for safety around children.
Motor size matters more than most buyers expect. A small motor jams on fibrous scraps and struggles with a busy kitchen, while a larger one grinds more finely and runs quieter. Look at the noise insulation and the grind chamber material as well, since stainless steel parts resist corrosion better than coated ones.
Caring for the unit after installation
- Run a steady stream of cold water before, during and for about 15 seconds after grinding.
- Feed scraps in small amounts rather than one large load.
- Keep grease, coffee grounds in bulk, fibrous vegetables and bones out of the unit.
- Never put your hand inside, and use tongs or the hex key at the bottom to free a jam.
- Grind a few ice cubes now and then to knock loose residue from the chamber.
If the unit hums but does not spin, it is jammed, not dead. Turn off the power, work the hex key at the base back and forth and press the reset button on the underside. If it keeps tripping, call us before the motor burns out.
Local wiring and drain surprises
Older kitchens sometimes hide surprises under the sink. The drain may be a different size from the new disposal outlet, the trap may be too low for the new unit or the cabinet floor may have rot from slow leaks. Check these before you buy a unit, not after.
If the cabinet floor is soft, repair it first. A heavy disposal on a weak floor loosens joints over time, and the leak that follows is hard to trace to its cause.
Prefer to have a plumber install it?
Call and we will schedule a visit.
Disposals in Marlboro kitchens
Marlboro kitchens are often large, with islands and second sinks, so the disposal under the main sink may be doing a lot of work. The township does not publish a rule we can quote on whether a disposal needs a permit, so permit rules vary. Ask the Marlboro Township Construction Division at (732) 536-0200, extension 1800, if you are changing wiring or drain lines.
Marlboro Township's water comes from its own wells and from Middlesex Water Company, according to the township's 2025 Water Quality Report. That does not change how a disposal works, but it is a good reason to run cold water while the unit operates.
Questions homeowners ask
If there is already an outlet or a hardwired connection under the sink, you often do not. If there is not, adding one is electrical work, and a licensed professional should do it.
A straightforward swap often takes one to two hours. Adding a disposal where there was none takes longer.
The most common causes are a flange that was not sealed with putty, a loose mounting ring or a drain joint that was not tightened.
Many septic owners avoid them or use them sparingly because food waste adds solids to the tank. Ask your septic professional.
Permit rules vary, so ask the Marlboro Township Construction Division at (732) 536-0200, extension 1800.