Quick Answer:
If your bathtub drain gurgles while filling, the sound usually comes from moving air in the drain line. That air is either being displaced by water or forced through a blocked or poorly functioning vent. The noise can be harmless or a sign of a vent or partial clog—check other drains, note recent plumbing work, and run a few simple observation steps to narrow it down.
Why This Happens
There are two common causes for gurgling during fill:
- Air displacement: As the tub fills, water pushes air ahead of it in the drain. If air can’t escape through the vent, it moves past traps and creates bubbling or gurgling sounds.
- Venting issues or partial blockages: A blocked roof vent or a partial clog in the drain line can force air to find another path — often through other fixtures — which produces gurgling noises. This is different from a full clog, which usually causes slow drainage or backups.
A gurgle that involves other fixtures or a toilet can point to a shared venting or main line issue. If you notice your toilet making similar noises, that link often means the problem affects multiple fixtures. Also pay attention if the gurgling started right after any plumbing work—changes to traps, vents or pipe routes can introduce air or misalign vents and cause new gurgling.
Step-by-Step What to Do
1. Observe and reproduce the sound
- Fill the tub to a typical level and stop the water. Listen closely near the overflow and the drain while filling and right after you stop. Note whether the gurgle happens only while water flows or continues after you stop.
- Watch the water level in the tub and the overflow plate for bubbles or backflow.
2. Test other drains
- Run the sink or flush a toilet while the tub is filling. If those fixtures gurgle at the same time, it suggests a vent or shared line issue rather than an isolated tub trap problem.
- If only the tub gurgles, the issue may be in the tub’s trap or local trap arm.
3. Check recent plumbing work
- Think back: Did the noise begin after a plumber worked on the bathroom, kitchen, or roof vent? New gurgling after work often points to a vent that was disturbed, an incorrectly installed vent, or a trap reassembled improperly.
4. Try simple fixes you can do safely
- Clear visible hair and debris from the tub stopper and strainer.
- Use a plunger on the tub drain (create a good seal and plunge gently). If you get improvement, you may have cleared a partial clog.
- If comfortable, use a hand-held drain snake on the accessible portion of the tub drain to remove hair. Stop if you encounter resistance you can’t clear easily.
5. Observe after each step
- After any attempt, refill the tub to the same level and listen again. If the gurgle goes away, monitor for recurrence. If it returns or you see slow drainage, move to the next step or call a pro.
What Not to Do
- Do not pour chemicals immediately.
- Do not ignore recurring gurgling.
- Do not assume it’s always a clog.
When to Call a Professional
Call a plumber if you have any of the following:
- Gurgling in multiple fixtures or a persistent odor of sewage.
- Slow drainage that doesn’t improve after safe, simple attempts (plunging, removing visible debris).
- Gurgling that started after recent plumbing work, or if a repair involved the vent or main line.
- Repeated episodes that keep coming back. If you’re unsure, it’s better to get a professional assessment than to let a small issue become a bigger one.
For guidance on deciding the right time to call, read more about when to call a plumber.
Safety Notes
- Don’t climb onto the roof to inspect vents unless you are experienced and have proper fall protection—leave that to a pro.
- Avoid chemical drain cleaners; they can damage pipes and create hazardous fumes and complicate professional repair.
- If you see sewage backup, strong sewer gas odors, or slow drains throughout the house, stop DIY attempts and contact a plumber—these are signs of a mainline problem.
Common Homeowner Questions
- Why does my toilet make gurgling noises when the tub fills?
If the plumbing vents or drain lines are shared, air forced through those lines can cause a toilet to gurgle when the tub fills. See notes about a **toilet making gurgling noises** for more detail. - Will a plunger always fix the gurgling?
No. A plunger can clear minor, local clogs but won’t fix venting problems or deep blockages in the main line. - Is a gurgling tub an emergency?
Not always. It’s an issue worth checking—call a plumber if it’s widespread, smells like sewage, or keeps coming back.