How to Install a Garbage Disposal When You Have a Dishwasher
A step-by-step overview for a typical under-sink install, including the dishwasher hookup, the electrical decisions and the points where a licensed pro makes sense.
Installing a garbage disposal alongside a dishwasher comes down to five stages: mount the sink flange, connect power, remove the dishwasher knockout plug, hang the unit, then connect the dishwasher hose and the drain trap. A handy homeowner replacing an existing disposal can often finish in two to three hours; a first-time install with new wiring takes longer. Turn the circuit off at the breaker before you touch any wiring, and if there is no outlet or switched circuit under the sink yet, that part is a job for a licensed electrician.
The instructions below describe a typical install. Your disposal’s manual is the final word, because mounting systems, cord options and dishwasher inlet details vary by brand and model.
Before you start: three decisions
1. Is your power ready?
A disposal is either plugged into an outlet under the sink (often controlled by a wall switch) or hardwired into a junction box on the unit. If you are replacing an old disposal, you usually reuse what is there. If this is a first install and there is no outlet or switch, new wiring is needed. Rules on circuits, switches and GFCI protection in kitchens vary by the electrical code edition your area has adopted, so check with your local building department or an electrician rather than guessing.
2. Do you need a permit?
Many jurisdictions treat a like-for-like disposal swap as minor work, while new circuits or new drain connections may need a permit and inspection. A quick call to the building department settles it.
3. High loop or air gap for the dishwasher?
Some local codes require a countertop air gap; others accept a high loop in the drain hose. Find out before you start, because adding an air gap may mean drilling the sink or counter. Our guide to connecting the dishwasher drain hose compares the two.
What you need
- The disposal, its mounting assembly and manual
- Plumber’s putty (or the gasket the manufacturer specifies)
- Flathead and Phillips screwdrivers, hammer
- Channel-lock pliers and a bucket for the trap
- Hose clamp for the dishwasher hose
- Power cord kit if your unit is sold without a cord and you are plugging it in
- Wire nuts and a cable clamp if hardwiring, plus a non-contact voltage tester
- Hacksaw or tube cutter in case the discharge tube needs trimming
- Flashlight, towels, safety glasses
If you are building up a basic set of tools, our home repair tool kit list covers most of these.
Step-by-step
- Shut off the power to the disposal circuit at the breaker and confirm it is dead with a voltage tester. Unplug or switch off the dishwasher too.
- Remove the old drain parts. Disconnect the P-trap and any old disposal or strainer. Keep a bucket under the trap. To take off an old disposal, support it from below and turn its mounting ring; it will drop free, so hold its weight.
- Install the new sink flange. Clean old putty from the drain opening, press a rope of plumber’s putty under the new flange and seat it in the sink. From below, add the gasket, backup ring and mounting ring, then tighten the mounting screws evenly until the assembly is firm. Wipe away squeezed-out putty. Some sinks and countertops call for a different sealant; check the sink maker’s guidance.
- Knock out the dishwasher plug. With the disposal on its side, tap out the plug in the dishwasher inlet with a screwdriver and hammer and fish the loose piece out of the chamber. Do this only if a dishwasher will be connected. See how to remove the knockout plug.
- Connect the power before hanging the unit, while the bottom plate is easy to reach. For a corded unit, attach the cord kit per the manual. For hardwiring, run the cable through a cable clamp, connect wire to wire by color (black to black, white to white) and the ground wire to the green ground screw. If any of this is unfamiliar, stop and hire an electrician.
- Hang the disposal. Lift it onto the mounting ring and turn the lower ring until the tabs lock. The manual shows the exact motion for your mount.
- Attach the discharge tube and line it up with the trap. Trim or extend it so the trap fits without strain.
- Reconnect the P-trap and tighten slip nuts by hand plus a small turn with pliers.
- Connect the dishwasher drain hose to the disposal inlet with a high loop or through the air gap, and secure it with a clamp.
- Leak-test before you restore power. Fill the sink partly, then pull the stopper and check the flange, the trap and the dishwasher connection with a dry paper towel.
- Restore power and test run with cold water flowing. Then run a short dishwasher cycle and watch the hose connection while it pumps out.
Common snags
| Problem | Likely cause | Fix |
|---|---|---|
| Dishwasher will not drain after install | Knockout plug still in place, or kinked hose | Remove the plug; straighten and re-route the hose |
| Drip at the sink drain | Flange not sealed or mounting screws uneven | Reseat the flange with fresh putty; tighten evenly |
| Discharge tube does not line up with trap | Trap arm height differs from the old unit | Trim or extend the tube; adjust trap; do not force joints |
| Disposal will not start | Breaker off, switch wiring, or reset button tripped | See disposal not working after reset |
What it typically costs
As of 2026, national cost guides from home-services platforms put professional labor for a straightforward disposal install at roughly $140 to $270, with full replacement including the unit often landing somewhere between about $200 and $625. New wiring, a new switch or reworked drain lines push the price higher. These are typical ranges and vary a lot by region, so get a written quote.
When to call a pro
- Licensed electrician: no outlet or switch under the sink, aluminum or damaged wiring, or any doubt about the circuit.
- Plumber: drain lines that are corroded or too low for the trap, a required air gap that needs a new hole, or a dishwasher that also needs a new water supply line.
- Either: if your area requires a permit and inspection for the work.
Doing your own install can affect warranty coverage on some products if instructions are not followed, so keep the receipt and follow the manual step by step. InSinkErator publishes its installation steps on its official support site; other brands provide similar guides with each unit.
Bottom line
Most of the work is ordinary drain plumbing. The two disposal-specific traps are the dishwasher knockout plug and the electrical hookup. Remove the plug before you hang the unit, have the power confirmed off, and leave new wiring to an electrician.
FAQ
Can I install a disposal on any sink?
Most standard kitchen sinks with a 3.5-inch drain opening accept a disposal. Check the clearance under the sink and the height of the drain pipe in the wall, since a disposal sits lower than a basket strainer.
Does the disposal need its own circuit?
That depends on the unit’s current draw, the other loads on the circuit and your local code. The disposal’s manual lists electrical requirements; an electrician can confirm whether your existing circuit qualifies.
Can I reuse the old mounting assembly?
Only if the new disposal is designed for it. Some brands keep the same mount across models, which makes swaps faster. Otherwise install the new mount that comes in the box.
How do I know if the install is leaking?
Leave dry paper towels on the cabinet floor for a day or two after the install. Any drip shows up clearly and points you to the joint above it.
