Quick Answer:
If grease keeps coming back after you clean the drain, the clog is likely deeper than surface debris or sitting in the trap and pipe walls. Removing and cleaning the trap and using mechanical cleaning or a targeted cleaner usually solves it. If the problem persists, the grease may be further down the line or in the sewer connection and needs professional attention.
Why This Happens
Grease and fat melt when hot water passes through, then re-solidify as they cool. That creates a thin, sticky layer on pipe walls that builds up over time. Simple surface cleaning often removes only what’s loose near the opening. If your routine changes — a different detergent or more dishwasher use — that can affect how grease and suds move through the drain. For situations tied to product changes, see Kitchen sink slow after switching detergent. If the dishwasher is related, check Drain slows after dishwasher use.
Step-by-Step What to Do
1. Start with a quick check
- Run hot water and observe how the drain behaves. Note slow drainage, gurgling, or backups into the dishwasher or nearby fixtures.
- Smell for sewer or stale odors that suggest trapped grease or trapped waste.
2. Remove and clean trap to check grease buildup
Place a bucket under the P-trap, loosen the slip nuts, and remove the trap. Empty its contents into the bucket and scrape away grease. Clean the trap with hot water and a brush, then reassemble temporarily and test the drain.
3. Inspect beyond the trap
- If the trap is clean but the drain is still slow, use a hand auger (plumber’s snake) to reach further into the drain. Feed it slowly and pull back debris as you go.
- If you see flaky or greasy rings on the cable, that indicates buildup on pipe walls.
4. Flush with hot water, not harsh mixing
After mechanical cleaning, flush with sustained hot (not boiling) water to help move softened grease. Do not mix chemicals — if you used an enzyme cleaner earlier, follow its directions and avoid mixing with other products.
5. Consider enzyme or biological cleaners
Enzyme-based products designed for grease can help break down residues over time. Use them per the label and allow enough contact time — they work slower than caustic chemicals but are safer for pipes and septic systems.
6. Reassemble and monitor
- Put the trap back together and run water, testing for leaks and drainage speed.
- Repeat the mechanical cleaning and enzyme treatment if some improvement occurs but the problem returns.
What Not to Do
- Do not assume surface cleaning fixes grease.
- Do not pour boiling water into plastic pipes — very hot water can soften plastic fittings. Use hot tap water instead.
- Do not mix different chemical cleaners. Combining products can be dangerous and damage plumbing.
- Do not repeatedly pour strong caustic drain openers down the sink as a long-term fix — they can harm pipes and fixtures and are often only a temporary solution.
When to Call a Professional
- Multiple drains are affected at once or your yard has sewage backups — possible sewer-line issue.
- Mechanical cleaning and trap cleaning don’t improve flow, or the clog is beyond the reach of a hand auger.
- You find recurring, heavy grease accumulation quickly after cleaning — a professional can inspect pipe runs or your sewer connection with a camera.
Safety Notes
- Wear gloves and eye protection when handling the trap or using tools. Grease and waste can contain bacteria.
- Work in a well-ventilated area if you use any cleaners. Read and follow product labels exactly.
- Collect trap contents in a bucket and dispose of them in the trash per local rules; do not pour greasy waste back down drains or into storm drains.
- If you are uncomfortable with plumbing work, call a licensed plumber instead of forcing fittings or digging into the sewer line yourself.
Common Homeowner Questions
How long will enzyme cleaners take to work? — They often need several applications over days to weeks to reduce grease buildup.
Can I prevent grease build-up? — Wipe pans and pour cooled grease into a can for disposal; avoid putting fats and oils down the sink.
Will boiling water clear a grease clog? — Boiling water can help loosen grease but may not reach clogs deep in the line and can damage some pipe materials; use hot tap water instead and combine with mechanical cleaning for best results.