Quick Answer:
If the sink only stops when water runs a long time, it often means a partial blockage or a venting issue that builds up pressure and briefly restores flow. Do a short set of checks, listen for gurgles, clear the trap if safe, and test again before trying stronger fixes.
Why This Happens
When a sink runs normally at first but only stops after running for a long time, one of these is usually true:
- Partial blockage in the trap or drain slows flow and allows air pockets to form.
- P-trap or drain venting problems let air get trapped and then release, causing variable flow and gurgles.
- Build-up from hair, grease, soap scum, or shaving residue narrows the pipe over time.
- Multiple fixtures sharing a drain can back up or change the pressure when flow is steady for minutes.
For patterns tied to specific activities, see Drain stops after shaving or symptoms that match air problems like Sink drains then gurgles.
Step-by-Step What to Do
1. Quick visual and smell check
- Look under the sink for leaks or a loose trap.
- Note any sewer odors or slow draining in other fixtures—this points to a main line issue.
2. Run a controlled test
Run water 5 minutes and listen for changes in pitch or gurgle. Pay attention to when the flow drops or when you hear suction noises.
3. Clear the P‑trap
- Place a bucket under the trap, loosen the slip nuts, and remove the trap to clear debris.
- Clean the trap and reassemble carefully, checking for leaks.
4. Try a plunger or small drain snake
- Use a cup plunger on the sink (seal overflow if present) to dislodge soft blockages.
- A handheld drain snake can reach a few feet beyond the trap to remove hair or gunk.
5. Rinse and retest
- Run the same 5‑minute test again and listen for changes.
- If flow still drops only after long runs, the restriction may be farther in the system or the venting needs attention.
What Not to Do
- Do not run the sink continuously if it consistently stops after long use.
- Avoid pouring strong chemical drain cleaners into a partially clogged sink—they can damage pipes and are hazardous if you later work on the trap.
- Don’t force or hammer pipes or fittings; that risks damage and leaks.
When to Call a Professional
- Multiple fixtures are slow or gurgling—possible main line or vent issue.
- Water backs up into other drains or the sink fills quickly after a short run.
- You find a sewer smell, persistent leaks, or you’re uncomfortable taking the trap apart.
- After DIY steps, the problem returns or gets worse.
Safety Notes
- Wear gloves and eye protection when working under the sink.
- Put a bucket under the trap before opening to catch water and debris.
- Do not mix chemical cleaners, and avoid them if you plan to manually clear the trap—residual chemicals are dangerous.
- Turn off water to the sink if a leak develops while you work.
Common Homeowner Questions
- Why does it gurgle? Air trapped in the drain or a blocked vent causes gurgling as water forces air through tight spots.
- Can I fix this with a snake? Often yes for shallow blockages; deeper or structural issues need a pro.
- Will running hot water help? Hot water can clear grease but won’t fix hair or solid build-up deep in the line.