Quick Answer:
If the disposer runs but the sink drains slowly, grease or a slimy buildup in the trap or just beyond it is often the cause. Start by running a strong stream of cold water while the disposer runs, then check and clean the P-trap before attempting deeper snaking. If the slowdown remains after those steps, call a plumber.
Why This Happens
When food scraps, fats and oils go down the drain they can cling to the inside of the drain and P-trap. Warm water or attempts to flush grease can make it smear and stick farther down. A running motor may chop solids but won’t clear a greasy coating inside the trap or the drain line. Over time that coating narrows the pipe and slows the flow, causing the sink to empty very slowly even though the disposer spins.
Step-by-Step What to Do
1. Start with cold water and run the disposer
- Switch to a strong cold water flow while running the disposal to keep grease solid. Cold water helps solids stay solid so the disposer can break them up rather than creating a greasy paste that clogs further down.
- Let the disposer run for 20–30 seconds with the cold water at full force, then keep water running a few seconds after turning the disposer off to flush the line.
2. Inspect and remove the P-trap
- Place a bucket under the trap (the curved pipe under the sink). Use channel-lock pliers or a wrench to loosen the slip nuts. Remove the trap and look for greasy buildup or a slimy coating.
- Check the trap for greasy buildup; if the trap is coated, clean/replace and retest before deeper snaking. Clean with a brush and hot (not boiling) soapy water, or replace the trap if it’s heavily corroded or permanently gunked.
3. Retest the drain
- Put the trap back in place, tighten the connections by hand and with a wrench so they are snug but not over-tightened. Run strong cold water and run the disposal to see if the flow returns to normal.
4. If it’s still slow, try a short auger beyond the trap
- If cleaning the trap didn’t fix it, use a 1/4″–3/8″ hand auger to snake the horizontal section beyond the trap. Do this gently and avoid forcing the cable hard against resistance.
- After snaking, reassemble and retest with strong cold water and the disposer running.
5. Persistent problems or recurring slow drains
- If the drain remains slow after these steps, stop and get professional help rather than using repeated chemical treatments or aggressive power tools that could damage the piping or disposer.
What Not to Do
- Don’t switch to boiling water to melt grease in PVC drains—heat can damage joints.
- If grease is suspected and slow drain persists, a plumber is appropriate; don’t keep dumping hot water or harsh chemicals down the line hoping it will clear.
- Don’t reach into the disposer with your hand while it’s plugged in or the power is on.
When to Call a Professional
Call a plumber if:
- The trap is clean and you still have a slow drain or backups.
- The disposer hums but won’t grind, or the motor runs without improving flow.
- There are frequent clogs, leaks at the trap connections, or signs of sewer backflow.
For related situations check these help pages: Disposal works but sink overflows and Disposal drains slowly after repair for guidance on overflow and post-service slow-drain scenarios.
Safety Notes
- Always disconnect power to the disposer before working on it — unplug or switch the circuit breaker off.
- Wear gloves and eye protection when removing the trap or dealing with sludge.
- Use the proper tools and avoid using excessive force on plastic fittings to prevent cracks and leaks.
Common Homeowner Questions
- Why use cold water? Cold water keeps fats and grease solid so the disposer can break them up instead of forming a greasy paste that clogs pipes.
- Will chemical drain cleaners help? They may offer a temporary fix but can damage pipes and the disposer and are not recommended for grease clogs.
- How long should I try DIY before calling a plumber? If cleaning the trap and a short hand-augur pass don’t restore normal flow, call a plumber rather than continuing trial-and-error.