Quick Answer:
After cooking, hot grease can flow down the drain, then cool and stick to pipe walls. That cooled grease traps soap and food debris, which can cause sudden flooding later. Immediately wipe up grease residue, avoid flushing any more grease, and run a strong stream of cold water while you assess the situation. Check the trap and the first short horizontal runs for buildup; if the problem repeats or you can’t clear it, call a plumber to snake or hydro-jet the line.
Why This Happens
Grease behaves differently at different temperatures. When hot, it moves easily and goes down the drain. As it cools it becomes sticky and solid, clinging to the inside of pipes—especially on horizontal sections where flow slows. Over time that film catches soap scum and food particles, forming a partial plug that lets water back up or suddenly give way and flood the sink.
If your situation looks like a case of Kitchen sink overflows suddenly or a frequent backup where the drain does not warn you first, grease buildup is a common cause.
Step-by-Step What to Do
1. Stop adding grease and clean visible residue
- Do not pour more grease, oil, or greasy water down the drain.
- Use paper towels to wipe pans, the sink basin, and the countertop. Dispose of the towels in the trash.
2. Run strong cold water while you assess
- Turn on a strong stream of cold water at the faucet to keep existing grease as solid blocks so it won’t smear farther into the system while you work.
- Cold water helps keep the grease in place so you can safely inspect and remove it from the trap and immediate pipes.
3. Check and clean the P-trap
- Place a bucket under the trap to catch water, turn off the disposal power if applicable, then loosen the slip nuts and remove the trap.
- Inspect for greasy bands, clumps of debris, or soap buildup. Wipe or scrape residue into the bucket and rinse the trap with cold water before reassembling.
4. Inspect short horizontal sections
- Look as far back as you can with a flashlight. Grease often builds in short horizontal runs where flow slows.
- If you can reach and safely remove grease, do so with gloves and a disposable rag. Keep cold water running to limit movement of softened grease.
5. Try a plunger or a small hand auger for minor clogs
- A sink plunger can dislodge a soft plug; use a few firm pumps while keeping the water level high enough to seal the plunger.
- A hand auger (plumber’s snake) designed for sinks can reach clogs just beyond the trap. Don’t force the snake; if it won’t move, stop and call a pro.
6. When the problem persists
- If backups continue after cleaning the trap and nearby pipes, or if multiple fixtures are affected, it’s time to contact a plumber.
- A professional can snake or hydro-jet the line properly to remove grease deposits further down the sewer line.
What Not to Do
- Don’t flush grease, soap scum, or pan drippings to ‘clean up’—it coats the line; if grease-related overflows repeat, a plumber is appropriate.
- Don’t rely on unlimited hot water to “wash it away.” Hot water can push grease deeper where it later cools and causes a worse clog.
- Don’t use strong chemical drain cleaners in an attempt to dissolve thick grease. They can be hazardous, damage finishes, and often don’t remove the hardened cake of grease.
When to Call a Professional
- Repeated backups or overflows after cleaning the trap and immediate pipes.
- Slow drainage in other fixtures (bathtub or other sinks), foul sewer smells, or sewage backing into the house.
- If you can’t reach the clog, or you suspect grease farther down the line—a plumber can snake or hydro-jet the pipe properly to clear grease buildup.
Safety Notes
- Wear gloves and eye protection when working under the sink. Grease and water can be slippery and messy.
- Turn off power to the garbage disposal before working on or near it.
- Keep children and pets away from the work area and from contaminated rags or waste buckets.
- Dispose of greasy rags and paper towels in the trash, not the recycling. Do not pour collected grease back into the sink or toilet.
Common Homeowner Questions
- Why did this happen hours after cooking? Grease may have flowed down while hot, then cooled and adhered to the pipe. Later water or dislodged debris can cause a sudden backup.
- Will pouring boiling water fix it? Briefly flushing with hot water can soften grease but risks pushing it deeper; cold water to stabilize the grease is safer while you inspect.
- Can I clear it myself every time? You can clean the trap and try a plunger or hand auger for small clogs, but repeated grease buildups need a plumber for a thorough snake or hydro-jet.
If the sink is currently flooding and you can’t stop it, shut off water to that faucet at the valve under the sink (if available) and call a professional if needed.
For related problems, consider reading about Sink backs up with no warning to learn more about sudden backups and their causes.
For more related articles, see the Kitchen Sink Overflows & Sudden Backups hub.