A couple of weeks back, my kitchen sink started making some weird gurgling noises every time I ran the garbage disposal. I ducked under the sink to investigate and found the problem: the unit was 13 years old and leaking right from the bottom.
Not exactly the highlight of my week, but I wasn’t about to throw $200 at a plumber for something I could probably fix. Well, as it turns out, knowing how to install a garbage disposal is less “rocket science” and a bit more “IKEA assembly with fewer swear words.”
What You’ll Need: Tools and Materials
(It takes around 2 to 3 hours for most homeowners)
- New garbage disposal. 1/3 HP for light use, 1 HP for heavy grinding, or you can match your last one if you are changing it. Septic system? Grab a septic-safe model.
- Screwdrivers (Phillips and flathead)
- Adjustable pliers or pipe wrench
- Plumber’s putty or silicone caulk
- Wire nuts and electrical tape
- Hacksaw (for trimming pipes, if needed)
- Bucket and towels (for water cleanup)
- Flashlight (because under-sink lighting is always terrible)
There are two main types of garbage disposals to choose from. Check out our guide to the differences between batch feed and continuous disposals to learn more.
Step 1: Turn Off the Power and Water
Safety first. Head to your circuit breaker and turn off the power to the disposal. If you’re not sure which switch controls it, turn off the main kitchen circuit. Test the disposal switch to make sure it’s off. I always double-check with a voltage tester to be extra safe.
Next, shut off the water supply under the sink. You don’t want any surprises while you’re working.
My tip: Shut off the sink’s water valves too. Mine were crusty and stuck, so I hit them with WD-40 and a wrench. Still leaked a bit—hence the bucket and towels I shoved underneath.
Step 2: Remove the Old Disposal (If You Have One)
Disconnect the plumbing: Place a bucket under the P-trap and loosen the connections with pliers. Remove the drainpipe and dishwasher hose. Be careful because there’s always some water left in the pipes, so keep those towels handy.
Detach the disposal: Use a screwdriver or disposal wrench to rotate the mounting ring counterclockwise. Firmly support the unit with your other hand because it’s heavier than it looks. If it’s stuck, try tapping the wrench with a hammer for extra leverage.
Clean the mounting area: Scrape off any old plumber’s putty from the sink flange. A plastic putty knife works great for this, but an old credit card will do in a pinch.
My old disposal was fused to the sink. The “wrenchette” (that goofy L-shaped metal bar that comes with disposals) felt a bit flimsy, so I jammed a screwdriver into the lugs for leverage.
My tip: If the discharge pipe won’t budge, heat the PVC nut with a hair dryer for about 10 seconds. Softens the plastic so it twists off without cracking.
Need more details? We’ve got a full guide on How to Remove a Garbage Disposal.
Step 3: Prep the Sink Flange
Roll and press the putty: Roll a 1/2-inch rope of plumber’s putty and press the new flange into the drain hole. Don’t skimp on the putty because this is what keeps water from leaking under the sink.
For stainless steel sinks, use silicone caulk or a non-staining putty instead. Traditional oil-based plumbers’ putty contains linseed oil that can bleed out and stain marble, granite, or stainless steel sinks.
Press the new flange into place: Squeeze it until the putty oozes out. Wipe away the excess with a rag. I used a rag with a bit of rubbing alcohol to clean up the edges for a smooth finish.
Secure the mounting assembly: Slide the fiber gasket and backup ring onto the flange and tighten the screws little at a time, in a star pattern, just like lacing a sneaker, to keep things evenly and to avoid warking the flange.
Step 4: Mount the New Disposal
Align and twist: Lift the disposal to align with the mounting tabs. Loosen the mounting ring screws halfway first. This gives you wiggle room to adjust the tabs and then twist clockwise until it locks.
My tip: If you’re struggling, try using your knee to support the weight while you twist it into place.
Tighten the screws: Secure the disposal with a screwdriver but be careful as overtightening cracks the ring.
Step 5: Connect the Plumbing
Attach the discharge tube: Trim the tube with a hacksaw if needed and connect it to the disposal. The first time I did this, I eyeballed the cut and hacked off 2 inches too much. I had to buy another $5 extension pipe, so please learn from my mistake and measure twice.
Reconnect the P-trap: Hand-tighten the connections, then use pliers for a quarter-turn. Be careful not to over-tighten as PVC cracks easily. I recommend wrapping the threads with some Teflon tape to avoid any leaks.
My tip: If the pipes don’t line up perfectly, you need to loosen the other connections and adjust them slightly.
Install the discharge elbow: Don’t forget to slide in the new diamond-shaped elbow with the rubber baffle (that little flap stops sewer gas from creeping up).
Dishwasher hookup: Knock out the dishwasher inlet plug with a screwdriver and hammer. Secure the dishwasher drain hose with a hose clamp. I used a flathead screwdriver and tapped it gently with a hammer to pop the plug out.
Step 6: Wire the Disposal
Wire gauge matters: Cutters won’t really care, but your breaker will.
- For 15-amp circuits (common in older homes): You must use 14 AWG copper wire. These circuits can safely handle most 1/3 to 1/2 HP disposals drawing 4 to 6.5 amps.
- For 20-amp circuits (modern standard for kitchens): They require 12 AWG copper wire. This applies to all the wiring in the circuit, including the switches and outlets. These circuits can safely handle larger disposals like 3/4 HP or 1 HP models drawing 7 to 8+ amps.
Hardwire the connections:
If it’s hardwired:
- Match the black (hot) wire to black, white (neutral) to white.
- Connect the green (ground) wire to the green screw.
- Tuck the wires into the junction box and secure the cover plate.
Corded: Just plug it into a GFCI outlet.
Step 7: Look for Any Leaks and Test It Out
Turn water and power on.
Run cold water and flip the disposal switch: Listen for smooth operation and inspect all of the connections for leakages. I prefer to run it for a minute or two and check for any drips. Better to catch a leak now than later.
Vibration check: Balance a nickel on the sink rim. If it dances off, you should retighten the mounting bolts.
My tip: Once everything’s hooked up, toss a lemon wedge down the disposal to freshen it up. For a deep clean, follow our guide on How to Clean a Garbage Disposal.
Once it’s running smoothly, keep it that way. And if things go sideways, learn How to Reset a Garbage Disposal or How to Unclog a Garbage Disposal.
Find a Plumbing Pro Near You
If you’re the DIY type and want to tackle installing a garbage disposal yourself, go for it—but know that even small missteps (like a loose seal or wiring hiccup) can lead to leaks or electrical issues down the line.
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Main Photo Credit: Goedeker’s / Flickr / CC BY 2.0
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