Slow drain with gurgling sound

Gurgling bathroom sink with slow drainage

Quick Answer:

A slow drain that makes a gurgling sound usually means air is moving through the drain system where it shouldn’t. That often points to a partial clog or a venting problem. Start by listening to when the gurgle happens, clear the P-trap, try a plunger, and only proceed to snaking or professional help if those steps don’t fix it.

Why This Happens

Gurgling is the sound of air rushing through water in a trap because pressure is changing in the drain line. Two common causes are:

  • A partial blockage in the drain that slows water and traps air pockets.
  • A blocked or restricted vent (the pipe that runs to the roof) that prevents air from entering the system normally, so air is pulled through the trap instead.

The exact pattern of the gurgle gives clues: if it only happens when this sink drains, the clog is likely local. If it happens when other fixtures run (toilet, washing machine), that points to venting or a main drain problem. For related situations, see posts like Slow drain after winterization or Bathroom sink drains slower over time for details on causes that develop gradually or after seasonal work.

Step-by-Step What to Do

1. Note the timing

Listen carefully. Listen for gurgle timing during drain: does it gurgle only while the sink empties, or when other fixtures run? Write down what you hear — that information helps decide the next move.

2. Run water and try a basic plunger

  • Fill the sink partway with water (to seal the plunger cup).
  • Plunge firmly for 10–20 seconds, then test the flow.
  • If you have a double basin, seal the other side while plunging.

3. Check and clean the P‑trap

  • Place a bucket under the trap to catch water and remove the slip nuts with adjustable pliers or by hand if possible.
  • Clear hair and gunk from the trap and rinse it out; reassemble and test the drain.

4. Clear the tailpiece and pop-up assembly

Remove the sink stopper and inspect the tailpiece and pop-up rod area for buildup. Clean any visible debris and run water again.

5. Try a drain snake for the tailpipe

  • Use a hand auger (plastic or small manual snake) down the sink drain to remove clogs beyond the trap.
  • Do not force a large powered snake into a thin fixture line — if you meet strong resistance, stop and consider a pro.

6. Check other fixtures and vents

If the gurgle appears when other fixtures operate, check toilets and other drains for slow emptying. Do not climb onto the roof to clear a vent unless you are trained and equipped — roof vent issues are safer for a professional. Persistent system-wide gurgling usually means a vent or main sewer issue.

7. Test after each step

After each action, run a steady stream of water and watch for speed and sound changes. If the gurgling stops and flow returns to normal, you’re done; if not, move to the next step or call a professional.

What Not to Do

  • Do not ignore vent-related gurgle.
  • Don’t pour large amounts of strong chemical drain cleaners into the sink repeatedly — they can damage pipes and create hazardous fumes.
  • Don’t force tools, or climb on the roof without proper safety gear and experience to reach the vent.

When to Call a Professional

  • If multiple fixtures gurgle or drain slowly at once.
  • If you notice sewer smell, sewage backup, or water pooling around floor drains.
  • If you suspect a blocked roof vent or main sewer line (especially after DIY steps fail).
  • If you are uncomfortable disassembling traps, using a snake, or working around potentially hazardous buildup.

Safety Notes

  • Wear gloves and eye protection when handling debris or using tools.
  • Place a bucket and rags under the trap to catch spills.
  • Avoid mixing chemical drain cleaners with other cleaners or plunging right after pouring chemicals — fumes and reactions can be dangerous.
  • If you need a roof inspection, hire a pro rather than climbing on steep or slippery roofs.

Common Homeowner Questions

  • Why does the sink gurgle after I flush the toilet? A flushing toilet uses a lot of water and creates pressure changes; if the vent or main line is restricted, the sink trap will gurgle as air moves through it.
  • Can I fix this with a chemical drain cleaner? Not reliably. Chemicals might clear small clogs but can damage pipes and mask vent problems. Mechanical cleaning and inspection are better first steps.
  • How fast should a sink drain after fixing it? Water should clear at a steady, fast stream within a minute. If it’s still noticeably slow or gurgling, further action is needed.

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