Quick Answer:
A steady drip under the cabinet usually comes from a connection point near the disposal: a loose slip-joint, a worn gasket, or the mounting assembly. Start by locating the highest wet spot with a paper towel, shut power to the disposal, then test and tighten or replace the small parts you can access. If the leak is from the disposal body or motor housing, call a pro.
Why This Happens
Under-sink leaks often follow gravity, but the true source can be upstream. Common causes:
- Loose slip-joint nuts on the sink tailpiece or the P-trap.
- Worn or misaligned seals between the sink and disposal or between the disposal and drain—think of a aged rubber gasket.
- Mounting ring problems after installation changes or if hardware was overtightened or not seated correctly.
- Cracked or corroded drain pipes, or a leaking dishwasher hose connection.
Small issues are common and fixable; larger leaks from the disposal housing usually mean the unit needs repair or replacement. Look for the highest wet point first to trace the flow back to where the water begins.
Step-by-Step What to Do
1. Turn off power and clear the area
- Unplug the disposal or switch off the breaker to the unit. Never reach into a disposal that could receive power.
- Remove items from the cabinet and place a towel or tray to catch water.
2. Find the true source
- Use a paper towel to trace the highest wet point under the sink to find the true source. Wipe upward along pipes and fittings—where it stays wet or gets wet first is where the leak starts.
- Look at the sink flange, mounting ring, the garbage disposal body, the dishwasher connection, and the P-trap in that order.
3. Test with a controlled run
- With a helper at the faucet, run a small steady flow of water while you watch the areas you found. This helps confirm the source without flooding the cabinet.
- If you find the leak only while the disposal runs, power off before touching anything.
4. Tighten and reseat accessible fittings
- Hand-tighten slip-joint nuts and then give a quarter-turn with a wrench if needed. Don’t over-tighten plastic fittings.
- If a tailpiece or trap seal looks misaligned, loosen, reposition, and retighten so the seal sits evenly.
5. Inspect seals and the mounting
- Look for a torn or flattened rubber seal where the disposal connects to the sink or to the drain. A sagging or brittle seal often needs replacement—**Disposal gasket worn out** is a common reason for drips.
- If the leak appears at the mounting assembly after adjustments, check the mounting ring and hardware. In some cases you may notice a persistent drip after tightening—search for advice under **Leak after tightening mounting ring** if that happens.
6. Replace small parts if needed and retest
- Replace worn gaskets, slip nuts, or washers with matching parts from a hardware store. Reassemble and retest with a small flow of water.
- If the leak stops, monitor for a day to make sure it’s fully fixed.
What Not to Do
- Do not chase the drip at the lowest point until you find the highest wet spot first.
- Do not put your hand into the disposal, and do not power the unit while working under the sink.
- Avoid using excessive force or pipe dope on plastic fittings; that can crack parts and make leaks worse.
- Don’t rely on catch-all sealants as a first fix for a fitting that needs replacement—sealants can hide the real problem.
When to Call a Professional
- If the leak is coming from the disposal motor housing or from inside the unit—this often means the unit must be replaced.
- If you can’t locate the source after tracing the highest wet point, or if multiple fittings leak at once.
- If electrical wiring or corrosion looks unsafe, or if you’re uncomfortable working in the confined space under the sink.
Safety Notes
- Always disconnect power to the disposal before touching fittings or attempting repairs.
- Wear gloves and eye protection when working under the sink. Pipes can be sharp and water can spray.
- Keep the cabinet area dry while working to avoid slipping or electrical hazards.
Common Homeowner Questions
- Why is water pooling only when I run hot water? — Thermal expansion can reveal small gaps; follow the highest wet point to trace the source.
- Can I tighten the mounting ring myself? — You can tighten superficial mounting hardware, but stop and call a pro if the unit shifts or the leak persists.
- Is a leaking disposal worth repairing? — If the leak is from a replaceable seal or connection, yes; if it’s from the motor housing, replacement is usually the best option.