To install a garbage disposal, mount the flange, hang the unit, connect drain and power, then test for leaks and jams.
New sink? Old unit died? This guide walks you through a clean, code-aware install that most handy homeowners can finish in an afternoon. You’ll see the parts, the steps, the wiring choices, and the gotchas that trip people up. If you searched “how to install a garbage disposal,” you’re in the right place.
Tools, Parts, And What Each One Does
This broad checklist helps you stage everything before you crawl under the sink. Grab what you need, then lay it out on a towel near the base cabinet.
| Item | Use | Notes |
|---|---|---|
| Disposal Unit + Mount Kit | Grinds food waste and hangs under the sink | Confirm horsepower and mount style match your sink |
| Plumber’s Putty | Seals the sink flange | Use a pea-thick rope; some sinks prefer silicone |
| Screwdrivers (Flat/Phillips) | Mounting ring, electrical cover, hose clamps | Medium sizes work for most units |
| Adjustable Wrench & Channel-Lock Pliers | Tighten slip nuts and compression fittings | Keep a rag for grip and drips |
| P-Trap Kit (1-1/2") | Completes the drain path | Use a standard P-trap, not an S-trap |
| Dishwasher Hose & Clamp (if used) | Routes dishwasher discharge to disposal | Knock out the inlet plug before attaching |
| Wire Stripper & Wire Nuts | Connect hot/neutral/ground (hardwire units) | Match wire gauge to circuit |
| 14/2 or 12/2 Cable or Cord Kit | Power connection (hardwire or plug-in) | Use a listed strain relief |
| Basin Wrench (nice to have) | Reach the mounting ring in tight spaces | Helpful on deep sinks |
| Bucket & Towels | Catches water from old trap | Have a sponge nearby |
Before You Start: Safety And Local Rules
Cut power to the kitchen sink circuit at the breaker. Verify with a non-contact tester at the receptacle or junction box. If you’re swapping sink hardware, shut the water supply valves too.
Many kitchens use a switched receptacle under the sink. Some are hardwired. A GFCI device reduces shock risk near sinks; a GFCI outlet or breaker trips fast when a fault occurs. Local code may set placement and protection rules, so check your city’s site or permit office page before you begin.
How To Install A Garbage Disposal: Step-By-Step
Set a timer, put on gloves, and work in this order. The mount comes first, then the body, then drain and power, then the test.
1) Remove The Old Drain And Prep The Sink
- Place a bucket under the trap and unscrew the slip nuts. Pull the trap and tailpiece. Wipe the sink drain opening clean.
- Roll a rope of plumber’s putty and circle the underside of the new sink flange. Press it into the drain opening from above.
- From below, stack the fiber gasket, backup ring (if included), and mounting ring per your kit. Tighten the three screws a few turns each in rotation so the flange seats evenly. Wipe away squeezed putty on top.
2) Hang The Disposal On The Mount
- Lift the unit and line up the ears on the mounting ring. Twist until it locks. Most brands use a twist-on “ring” that tightens with a supplied wrench or a screwdriver in the lugs.
- Do not connect the discharge tube yet. Keeping it loose helps you align the trap later.
3) Choose Your Power Path: Plug-In Or Hardwire
Most modern units ship “ready for either.” Pick the method that matches your kitchen and follow the label inside the electrical cover plate on your unit.
Plug-In Method
- If your cabinet already has a switched receptacle, install the cord kit that matches your model. Route the cord through the strain relief into the wiring cavity, then connect black to hot, white to neutral, and green to ground. Replace the cover plate.
- Plug into the switched receptacle. Leave the switch off for now.
Hardwire Method
- Shut the breaker. Remove the electrical cover plate. Add a listed cable connector to the knockout on the base.
- Feed NM-B cable through the connector. Connect black to the unit’s black lead, white to white, bare/green to ground screw. Cap with wire nuts. Tug-test each splice. Reinstall the cover plate.
4) Connect The Dishwasher (If Present)
Dishwashers drain into the disposal through a small side inlet. New units ship with a knockout plug in that port. Remove it first, then attach the hose with a clamp.
- Insert a screwdriver into the inlet and tap with a hammer to knock out the plug. Remove the loose disk from inside the unit.
- Slide the hose on and tighten the clamp. If your area requires a deck-mounted air gap, route the hose through that device as shown on the package.
If you see a drip at this joint later, double-check the plug removal and clamp tension. InSinkErator’s help page on the dishwasher inlet shows the knockout and common fixes.
5) Set The Discharge Tube And P-Trap
- Attach the discharge elbow to the disposal outlet with the supplied metal band. Point it toward the wall drain.
- Dry-fit the 1-1/2" PVC trap kit: disposal elbow → trap inlet → trap arm → wall stub. You may need the short straight tailpiece that came with the unit.
- Aim for a gentle slope on the trap arm toward the wall. Keep the trap below the sink outlet and above the wall’s centerline so you don’t create an S-shape.
- When aligned, add the slip-joint washers (taper toward the joint) and tighten the nuts hand-tight plus a quarter turn with pliers.
6) Final Tightening And Alignment
- Turn the mounting ring until the unit feels solid. The discharge should not bind the trap.
- Snug the band clamp at the disposal outlet and all slip nuts on the trap.
7) Leak Test And Power-On Test
- Stopper the sink and fill it halfway with cold water. Pull the stopper and watch every joint with a flashlight. Wipe suspected joints with a dry tissue to spot thin leaks.
- Restore power. Run cold water. Flip the wall switch for a 5-second spin. Feed a few ice cubes to confirm grind and flow. No rattles, no leaks? You’re set.
Installing A Garbage Disposal With A Dishwasher Hookup
If your sink serves a dishwasher, that short hose must reach the disposal’s inlet without a sag that traps food. Keep a high loop under the counter or use an air gap where required. Knock out the inlet plug first. Then clamp both ends snug. A smooth, kink-free run helps the dishwasher clear water at the end of each cycle.
Electrical Details That Save Headaches
Many kitchens use a switch on the backsplash that controls a receptacle under the sink. A GFCI device adds protection where water and electricity share space. OSHA’s page on ground-fault circuit interrupters explains how these devices cut power fast when a fault occurs. If you swap a standard outlet for a GFCI, label the downstream receptacle if it’s fed from the GFCI’s “load” terminals.
Hardwiring? Use a listed cable clamp and keep splices inside the unit’s wiring cavity. Black to hot, white to neutral, green/bare to ground. If the cable sheath must pass through sheet metal, a bushing or connector protects the jacket.
Common Measurements And Clearances
Clear space makes the install smoother. Here’s a quick reference people ask for all the time:
- Sink opening: Standard 3-1/2" diameter.
- Cabinet depth: Most compact units fit a 24" base; tall bodies may need a shorter trap arm.
- Trap height: Keep the trap weir below the sink outlet and above the wall stub center to avoid siphon issues.
- Dishwasher hose: Use a loop high under the counter or an air gap if your area calls for it.
Troubleshooting And Quick Fixes
Ran into a snag? Use this table to spot the cause and the usual fix.
| Problem | Likely Cause | What To Do |
|---|---|---|
| Unit hums, no grind | Jammed flywheel | Kill power; insert the hex key in the bottom socket and twist both ways; press reset, retry with water |
| Water drips at sink | Loose flange or thin putty | Back off mount, reseat flange with fresh putty, retighten evenly |
| Leak at dishwasher inlet | Knockout still in place or loose clamp | Remove the plug; tighten the clamp; trim hose to a smooth path |
| Backflow into dishwasher | No high loop or air gap | Add a high loop or install a code-approved air gap |
| Slow drain | Trap sag or long flat run | Realign trap with slight downhill to wall; shorten trap arm |
| Trips breaker | Locked rotor or short | Clear jam; check wiring; try a GFCI/AFCI protected circuit if required by your area |
| Vibration and rattle | Mount not fully locked, uneven grind ring | Tighten the mounting ring; rehang the body square to the flange |
Care Tips That Keep It Running
- Cold water always during use. It firms up grease and moves it along.
- Small loads only. Feed small scraps while the unit spins. Let the water run 10–15 seconds after the sound clears.
- Freshen the chamber. Ice chips scour the grind ring. Citrus peels add a clean scent.
- Avoid fibrous and hard items. No corn husks, artichoke leaves, bones, or loose pits.
- Check the trap yearly. A quick clean keeps flow strong.
Model Features That Affect The Install
Mount style and body size shape the steps above. Many InSinkErator units use a twist-on ring with “ears” you tighten as you lift the body into place. Their manuals show the knockout for a dishwasher hose, the ground screw location, and the wiring cavity layout. See the brand’s installation guide for diagrams that match your exact model.
When To Bring In A Pro
Hire a licensed plumber if your wall stub is too low or the venting is unclear. Call a licensed electrician if the cabinet has no switched receptacle, the breaker trips repeatedly, or you’re unsure about cable sizing. Small fixes are quick when a pro has the right parts on the truck.
Frequently Missed Details That Cause Do-Overs
- Knockout plug left inside. People forget to fish out the plug disk after knocking it loose. It rattles and blocks the impellers.
- P-trap alignment. A sagging trap arm or an S-shape leads to slow flow and odors. Keep a clean P-shape with a short arm to the wall.
- Loose ring screws. Tighten each screw a little at a time so the flange seats flat and stays sealed.
- No strain relief. Every cord or cable entering the wiring cavity needs a listed clamp so the splice isn’t stressed.
- Switch wiring crossed. If the switch controls the wrong receptacle, trace the feed and load conductors and label them.
What To Budget And How Long It Takes
Most DIY installs land in the 1–3 hour range. First-timers lean toward the long side while working methodically. Cord kit, trap kit, and putty add a small cost on top of the unit. If you’re swapping sink bowls or moving the wall stub, add time for that work.
Recap: You’ve Learned How To Install A Garbage Disposal
You mounted the flange, hung the unit, set the discharge and trap, chose a safe power path, hooked the dishwasher (if used), and ran a clean test. Bookmark this page and the brand’s manual. If a leak pops up later, the troubleshooting table above gets you back to normal fast.