Quick Answer:
If the slowdown returns after you clean a drain, something is still blocking flow or water movement. Start with simple checks, flush with very hot water only and recheck next day, then work through the trap, the vent and any nearby fixtures before you call a pro.
Why This Happens
Cleaning the visible part of a drain removes surface debris, but other things can keep slowing water down:
- Debris collected deeper in the P-trap or further down the line (soap, hair, grease, mineral buildup).
- A partial blockage beyond the trap that refills or compacts after a light clean.
- Vent or slope problems that let air or water sit in the pipe and slow drainage.
- Localized issues that create repeat problems, for example Hair buildup only in P-trap or Sink clogs only in upstairs bathroom.
Step-by-Step What to Do
1. Remove and inspect the strainer or stopper
- Clear any hair or gunk you can see. Use a gloved hand or a small brush.
- Run water briefly to see if the flow improves before moving on.
2. Flush with very hot water
- Flush with very hot water only and recheck next day.
- This can soften soap scum and move loose debris. Do not use boiling water on aged PVC piping—use caution (see Safety Notes).
3. Clean the P-trap
- Put a bucket under the trap, loosen the slip nuts, and inspect inside. Remove hair and solid buildup.
- Reassemble and test. If the trap was full of gunk, this often fixes recurring slow flow.
4. Check nearby fixtures and run tests
- Run water in other sinks, tubs or toilets. If multiple fixtures are slow, the blockage is farther down or in a branch line.
- Listen for gurgling or bubbling—this can indicate a vent problem.
5. Use a hand snake if needed
- If the trap is clean but the sink is still slow, a short hand auger can reach a little farther down the line to break up soft blockages.
- Avoid forcing a long or rigid tool; work gently to avoid damaging pipes.
6. Re-check after 24 hours
- Some partial clogs settle back after initial cleaning. Test the drain the next day. If it’s slow again, the root cause is likely deeper or structural.
What Not to Do
- Do not assume cleaning fixed the root cause.
- Don’t mix or pour chemical drain cleaners after a mechanical attempt—chemicals can be hazardous and may damage pipes.
- Avoid using excessive force with tools that can crack or deform piping.
When to Call a Professional
- The drain is slow again after you’ve cleaned the trap and flushed with hot water.
- Multiple fixtures are affected, or you smell sewage or hear constant gurgling.
- There are signs of a deeper problem (repeated clogs, backups, or water damage).
- If you’re not comfortable disassembling plumbing or using an auger, call a licensed plumber.
Safety Notes
- Wear gloves and eye protection when working on drains.
- Use a bucket under the P-trap to catch water and debris before loosening connections.
- Do not pour boiling water into PVC piping—use the hottest tap water or consult a professional if in doubt.
- Do not mix chemical products. If a chemical was used previously, be cautious opening traps or using tools until you’re sure it’s safe.
Common Homeowner Questions
- Why did the sink slow again after I cleaned it? A partial blockage deeper in the line, the trap refilling with debris, or a vent/pipe issue is still present.
- Will pouring boiling water fix it? Hot water may help; boiling water can harm some plastics—use caution and follow the flush step above.
- How long should I wait before calling a plumber? If the drain is slow again after cleaning and the hot-water recheck the next day, call a professional.