Your disposal leaks from the bottom. Here's why that's the end.
Where a disposal leaks tells you almost exactly what it will cost to fix. Three of the four common spots are a five-dollar repair. The fourth one isn't repairable at all.
The first thing to do with any disposal leak is stop guessing about it. Dry the whole unit and the cabinet floor with a towel, lay a sheet of paper towel underneath, run the water for thirty seconds, and look. Paper towel shows you the first drop and where it landed. Everything below depends on knowing which of four places the water is coming from.
Leak 1: from the top, where the disposal meets the sink
Cost: about five dollars.
The sink flange seal has failed. Plumber's putty dries out and shrinks over years, and the mounting bolts loosen with vibration.
Sometimes all it takes is evenly re-tightening the three mounting screws. If that doesn't do it: power off at the breaker, support the unit and twist it off the mounting ring, drop it, disassemble the mount, and scrape every trace of old putty off the sink. Roll a fresh rope of putty about half an inch thick, press the flange in until putty squeezes out all round, reassemble, and tighten the three screws a little at a time in a triangle rather than one at a time. Wipe the squeeze-out.
Leak 2: at the dishwasher hose
Cost: a few dollars, or nothing.
The hose clamp on the dishwasher drain connection loosens, or the rubber hose cracks with age. Tighten the clamp first; if the hose is stiff, cracked or ballooned near the fitting, replace it. Both are hardware-store parts.
Leak 3: at the discharge tube
Cost: five to twenty dollars.
Where the disposal connects to the P-trap there's a rubber gasket held by two bolts (or on some units a slip nut). Gaskets flatten and harden. Bucket underneath, undo the bolts, pull the elbow, fit a new gasket, and reassemble — snug, not gorilla-tight. The flange is soft metal and it will distort, which makes the leak worse.
While you're there, check the P-trap's own slip nuts. People replace a disposal over a leak that was actually the trap eighteen inches downstream.
Leak 4: from the very bottom of the motor housing
Cost: a new disposal.
Water dripping from the bottom centre of the unit — near or around the reset button — means the internal seal above the motor has failed. Water is getting into the motor housing. There is no serviceable part, no gasket kit, and no plumber who can fix it. Replace the disposal.
It's worth understanding why, because people don't believe this the first time they hear it. A disposal is a sealed grinding chamber sitting directly on top of an electric motor, separated by a shaft seal. That seal is a wear item. When it goes, water runs down the shaft into the windings — and it's a shock hazard as well as a dead machine. Manufacturers don't sell the seal separately because replacing it means splitting the unit, and by the time it's leaking the bearings have usually been running wet for a while anyway.
If you're seeing bottom leakage, switch the breaker off and leave it off until it's replaced. Don't keep using it because "it's only a few drops."
Two leaks that aren't the disposal
- Condensation. A cold metal disposal in a humid kitchen sweats. If the "leak" appears without the water running and the unit is uniformly damp rather than dripping from a point, that's what you have.
- The sink basket on the other side. Water tracks along pipes and drips off the lowest point, which is often the disposal — even when it started somewhere else entirely. This is exactly what the paper towel test is for.
The one-line summary
Top, side, or drain connection: fix it, cheaply, this afternoon. Bottom of the motor housing: it's finished, and the only question is which unit replaces it.
The step-by-step replacement guide walks the whole job, or see the units we'd actually buy. If you'd rather not spend a Saturday under a sink, we do this every day.