Quick Answer:
If the garbage disposal started leaking after you replaced the sink, the most likely causes are a bad flange seal, debris between the flange and sink, or a misaligned mounting assembly. Stop using the disposal, turn off power and water, then check the flange and mounting ring. Clean the sink opening, reseal the flange, and tighten the mount evenly while checking for leaks.
Why This Happens
Common reasons a disposal leaks after a sink replacement:
- Old plumber’s putty or gasket material left on the sink opening so the new flange can’t seal properly.
- The flange wasn’t centered or the mounting ring wasn’t tightened evenly, leaving a gap where water can escape.
- Debris or paint on the sink surface prevents a flush seal.
- Cracked or warped flange or sink material around the hole.
If the leak only shows with hot water, temperature can change seals or reveal a weak spot — see Disposal leaks only when hot water used. If the drip seems to come from below rather than at the flange, consider Disposal dripping under sink for troubleshooting focused on the connections under the unit.
Step-by-Step What to Do
Step 1 — Safety first: power and water off
- Turn off the disposal at the wall switch and flip the breaker to cut power to the unit.
- Shut off the shutoff valve for the sink or the home’s water main if there isn’t a local shutoff.
Step 2 — Inspect from above and below
- From above: remove any strainer, look at the flange seat and sink opening for putty, debris, or paint.
- From below: check the mounting assembly, gasket, and the lip where the flange meets the sink for wetness or gaps.
Step 3 — Clean and confirm the flange seal
- Remove old putty or gasket material. Clean the sink opening and flange mating surface with a rag and a mild cleaner; dry completely.
- Confirm the sink opening and flange are clean and properly sealed before tightening the mount. A proper seal might be plumber’s putty for a metal sink or the manufacturer’s gasket; use what the disposal instructions specify.
Step 4 — Re-seat the flange and tighten evenly
- Place fresh plumber’s putty or the gasket around the flange as instructed. Set the flange into the sink opening and press to seat it evenly.
- From under the sink, assemble the mounting ring and tighten the mounting bolts gradually and evenly in a star pattern so the flange stays centered.
Step 5 — Test carefully
- Restore water and power. Run water (start with cold), then inspect the seal for leaks. Try hot water as well to check for temperature-related failures.
- If you still see leaking, stop and re-check the seal and the tightness pattern. If the flange or sink hole looks damaged, stop and consider a replacement or calling a pro.
What Not to Do
- Do not tighten the assembly before confirming the flange is centered and the sink surface is clean.
- Do not overtighten in one spot — that can crack the sink or deform the flange and make leaks worse.
- Do not work on the unit with power connected or with your hands inside the disposal chamber.
When to Call a Professional
- If the flange or sink material is cracked, chipped, or warped so it won’t seat properly.
- If you can’t stop the leak after cleaning and reseating the flange, or if the leak comes from the disposal body rather than the flange.
- If wiring or electrical connections were disturbed during the sink replacement — call a licensed electrician for any electrical safety concerns.
Safety Notes
- Always cut power at the breaker before working on the disposal.
- Shut off the water and drain the sink before loosening plumbing joints.
- Wear gloves and eye protection when handling plumber’s putty, cleaning chemicals, or sharp metal edges.
Common Homeowner Questions
- Why does it leak only with hot water? — Hot water can soften old putty or expand gaps, revealing a weak seal.
- Can I use silicone instead of plumber’s putty? — Silicone works for some materials (like cultured marble) but check the disposal and sink manufacturer’s recommendations first.
- How long should a flange seal last? — With proper installation it should last years; inspect annually and after any sink work.