How to Install a Garbage Disposal
Direct-replacement disposal install: 45 minutes. New install (no existing): 90 minutes plus electrical.
TL;DR
Replacing an existing disposal is a 45-minute job with no electrical work needed (existing wires are reused). Installing a new disposal in a sink that didn’t have one requires running a new circuit (electrical permit) and adding a switch — usually pro work in LA.
What’s in this guide
- Replace vs new install
- Tools needed
- Disconnecting old disposal
- Mounting new unit
- Plumbing connection
- Testing
Garbage disposal replacement is one of the more accessible DIY plumbing projects if your sink already has a disposal. The wiring is reused, the mounting hardware is standardized across most brands, and the entire job runs 45–60 minutes. Adding a NEW disposal where one never existed is a different project requiring electrical work.
Tools & Materials You’ll Need
Tools
- Adjustable wrench
- Phillips and flathead screwdrivers
- Bucket
- Towels
- Voltage tester (for confirming power off)
- Allen wrench (usually included with disposal)
Materials
- New garbage disposal (Insinkerator, Waste King are the most common in LA)
- Plumber’s putty
- Replacement drain hose (if not included with new unit)
- New mounting gasket (usually included)
Step-by-Step Instructions
Turn Off Power and Verify
At your electrical panel, flip the breaker for the disposal circuit (often labeled “Disposal” or “Kitchen”). Use a voltage tester at the disposal switch under the sink to confirm power is off. Don’t skip this — disposals are wired hot and shock risk is real.
Disconnect Plumbing
Place a bucket under the disposal. Disconnect the discharge tube (the pipe leading to the P-trap). Disconnect the dishwasher hose if connected (small clamp). Loosen the disposal mount by rotating the locking ring counter-clockwise — sometimes requires a hammer tap to break loose.
Disconnect Electrical
On the bottom of the old disposal, unscrew the small electrical cover plate. Inside you’ll find black, white, and green/copper wires connected to the unit. Disconnect using wire nuts or terminal screws — note which wire goes where (color matching). Pull the wires out through the cable connector.
Install the New Mounting Assembly
New disposals come with a mounting collar that goes around the sink drain hole. Apply plumber’s putty around the new sink flange. Drop the flange into the drain hole from above. Underneath, slide on the rubber gasket, fiber gasket, mounting ring. Tighten the screws on the mounting ring evenly to seal the flange.
Connect Wiring on New Unit
Following the wiring diagram for your specific disposal, connect black-to-black, white-to-white, and ground (green or bare copper) to the green screw or ground wire. Use wire nuts (usually included). Tuck wires into the unit’s electrical chamber, replace the cover.
Mount Disposal to Sink
Lift the disposal up to the mounting collar (the part you installed in step 4). Rotate clockwise until it locks into place. Listen/feel for the click. The unit should hang securely without your support.
Connect Plumbing and Test
Reattach the discharge tube to the disposal output and to the P-trap. If you have a dishwasher, knock out the dishwasher inlet plug INSIDE the disposal (use a screwdriver and hammer — be sure to remove the broken plug from the disposal interior). Connect the dishwasher hose. Restore power. Run the disposal with cold water flowing for 15 seconds to test.
After installing 200+ disposals a year, the failure pattern is consistent: motor windings burn out from running with insufficient water flow, or the impellers seize from soft cheese, cooking grease, and avocado pits. The hex-key reset trick works for ~80% of jams; the other 20% need replacement because impellers have bent or motor windings have fried. If you’ve reset the unit twice and it still hums without spinning, stop trying — additional resets weld the magnetic-overload contacts shut and turn a $250 replacement into a panel-board electrical fix.
Knock out the dishwasher plug BEFORE connecting
New disposals come with the dishwasher inlet sealed (so the disposal can be installed without a dishwasher). If you have a dishwasher, knock the plug out FROM INSIDE the disposal. If you forget, dishwasher water has nowhere to go and backs up into the dishwasher.
Real Scenarios from Our LA Service Calls
Disposal install caused dishwasher flood
Homeowner installed new InSinkErator without removing the dishwasher inlet plug. Three days later, dishwasher water backed up and overflowed onto the floor. Called us thinking the dishwasher had failed. Diagnosis: the disposal plug was still in place. Knocked it out (5 minutes), problem solved. Total call: $185.
When to Call a Plumber Instead
DIY isn’t always the right call. Bring in a licensed plumber if any of these apply:
- Adding a disposal where one never existed (electrical work)
- Your existing disposal is hardwired to a switch you can’t locate
- You’re uncomfortable with electrical wiring
- The mounting collar in your sink is corroded
Frequently Asked Questions
How long does a garbage disposal last?
Budget unit (Waste King L-1001): 5–7 years. Mid-range (InSinkErator Badger 5): 8–12 years. Premium (Evolution Excel, Compact): 12–18 years. LA water hardness shortens these by 1–2 years.
1/3 HP, 1/2 HP, or 3/4 HP?
1/3 HP for studio/1-bedroom (light cooking). 1/2 HP for typical 2-bedroom homes. 3/4 HP for large families or homes with heavy cooking. 1 HP+ for commercial-style kitchens.
Do I need a dedicated circuit?
Yes — disposals require a 15A or 20A dedicated circuit. New installs need this electrical work done before plumbing.
Why does my disposal smell?
Food trapped in the splash guard or impellers. Run with cold water + ice cubes + lemon peels. Or remove the rubber splash guard and clean it (food gets stuck above the cutter blades where you can’t see).
What can’t go in a disposal?
Bones, fruit pits, fibrous vegetables (celery, asparagus, banana peels), grease, eggshells, coffee grounds (debatable but they accumulate). Best practice: scrape plates into trash, only RUN the disposal with cold water flowing.
Need professional help in Los Angeles?
Same-day service. Flat-fee pricing. No surprise add-ons.
Call (818) 938-8660
