Quick Answer:

If you hear a gurgling noise coming from the bathroom basin when the toilet is flushed, it usually means air is being pulled through the sink trap. That pull can come from a partially blocked drain, a restricted vent, or a shared drain line that isn’t flowing freely. The simplest first check is quick and safe to do yourself.

Why This Happens

Plumbing fixtures rely on trapped water in the sink P-trap to stop sewer gases and to keep flows balanced. When a large volume of water rushes down the toilet, it can create a pressure change in the shared drain or vent system. If air is forced or pulled through the sink trap during that event, you’ll hear a gurgle.

• Common causes: partial clog in the sink or toilet drain, a restricted or obstructed vent pipe, or a long shared drain run with poor slope.
• Less common causes: cracked trap, loose vent flashing, or debris in a house trap (if present).

If the symptom shows patterns—for example only at night—compare notes with the situation described in Bathroom sink bubbles at night to see if the timing or water use pattern matches.

Step-by-Step What to Do

1. Do a simple observation

Flush the toilet and watch the sink at the same time. Look closely at the trap under the sink or at the tail of the sink stream (if the trap is not visible) and note if the water level actually dips or moves. Flush the toilet and observe sink trap movement.

2. Check for slow drains or backups

• Run the sink and the toilet separately. Does the sink drain more slowly than usual? Does water back up into the sink when the toilet is flushed?
• If the sink drains slowly, try clearing the sink drain with a plunger made for sinks (use a sink stopper to seal the overflow, if present) before moving to stronger measures.

3. Clear accessible blockages

• Remove and clean the sink’s pop-up or strainer—hair and soap buildup are common causes of partial clogs.
• Use a hand auger (plumbing snake) only for the sink drain if you are comfortable; avoid over-forcing it.

4. Test again after simple fixes

After clearing debris and testing the sink drain, flush the toilet several times to see whether the gurgle persists. If the sound is gone, the problem was likely a partial clog or slow drain.

5. Consider venting and shared drain issues

If the gurgling continues even with a free-running sink drain, the issue may be a restricted roof vent or a problem further down the shared drain. At that point you may need a professional inspection or a camera evaluation.

What Not to Do

• Do not assume it is ‘normal’ if it happens with every flush.
• Avoid repeatedly pouring strong chemical drain cleaners into the sink. They rarely fix vent problems and can damage pipes or make future repairs hazardous.
• Do not attempt unsafe roof access to clear a vent unless you are trained and have proper fall protection—this is best left to contractors.

When to Call a Professional

• Persistent gurgling after you have cleared visible blockages and tested the trap.
• Water backing into the sink or toilet, repeated clogs in multiple fixtures, or smells of sewer gas.
• If you suspect a blocked vent stack or a mainline obstruction; these often need tools and a camera inspection that professionals provide.

Safety Notes

• Wear gloves and eye protection when working on drains or removing trap parts.
• If you use tools, follow the manufacturer’s directions and avoid forcing components that could break seals or crack pipes.
• If you smell strong sewer gas or see signs of sewage backup, stop and call a professional—exposure can be hazardous to health.

Common Homeowner Questions

• Will a plunger fix this? If the cause is a partial clog near the fixture, a plunger may help; if the issue is venting or a distant obstruction, a plunger usually won’t fix it.
• Can I use chemical drain cleaners? They are not recommended for recurring gurgles and can damage pipes or create hazards for anyone working on the plumbing later.
• What if it only gurgles sometimes? Intermittent gurgling can suggest a partial clog or a vent that sometimes traps air—see more on **Gurgling only sometimes** for patterns to watch.