Quick Answer:
If bubbles appear in the sink after a recent repair, it usually means the drain or venting was disturbed or a connection is letting air in. Start with a quick visual check under the sink for loose connections and the trap arm slope, then run a water test. Many causes are easy to fix; some require a plumber.
Why This Happens
Air can enter a drain system when a seal or joint is not tight, when the trap is dry or misaligned, or when venting is restricted. After a repair the technician may have loosened or removed the trap or the trap arm and not returned it to the correct position. You might also notice intermittent noises — think of Gurgling only sometimes — when vents or seals are partly blocked. Small bubbles are usually trapped air being pushed out as wastewater flows past a poor seal or an improperly sloped trap arm.
Step-by-Step What to Do
1. Gather basic supplies
- Bucket or bowl, flashlight, adjustable pliers, clean rag, gloves.
- Turn off the sink shutoff valves only if you plan to loosen fittings.
2. Visual check under the sink
- Look for wet spots, drips, or loose slip nuts at the P-trap and the trap arm where it meets the wall.
- Check that the trap arm (the horizontal pipe from the P-trap to the wall) slopes slightly downward toward the wall. If it slopes upward it can trap air and cause bubbling.
3. Check connection tightness
- Gently feel the slip nut joints. They should be snug but not crushed. If a nut is finger-loose, tighten it by hand until snug and give a small extra turn with pliers (about a quarter turn).
- Place a bucket under the trap first. If you need to remove the trap to inspect the seal, empty it into the bucket and check the washers and threads before reassembling.
4. Run a simple test
- Plug the sink, fill it with water, then release and watch for bubbles as the water flows. Also try running only the faucet briefly and observe whether bubbles appear while draining. This helps reproduce the issue and shows whether the trap is sealing properly.
- If you see bubbling with the faucet off or when other fixtures are used, note the timing — it can point to venting problems or blockages elsewhere. A common pattern is described by Sink bubbles when faucet off.
5. Re-seat washers and reassemble carefully
- If you removed the trap, inspect the flat washer and the seat. Replace any damaged washers before reassembly.
- Hand-tighten and check for leaks. If the leak stops and bubbling stops, you’re done. If bubbling persists, the vent or a branch line may need inspection.
What Not to Do
- Do not overtighten slip nuts trying to stop bubbling. Overtightening can crack plastic fittings or deform washers and lead to leaks.
- Do not pour strong chemical drain cleaners into a trap you plan to touch—these can splash and cause burns or damage fittings.
- Avoid removing more of the drainage system than you’re comfortable reassembling; if a joint looks corroded or stuck, stop and call a pro rather than forcing it.
When to Call a Professional
- Persistent bubbling after you’ve checked seals and slope.
- Any active leaks you can’t stop, visible cracks in drain pipes, or a damaged trap arm.
- Repeated backing up of water or sewer smell — these can indicate a venting problem or blockage further in the system.
Safety Notes
- Always put a bucket under the trap before loosening fittings. Wear gloves and eye protection if you expect waste water to spill.
- Turn off water supply valves if you will be disconnecting pipes. Know where the main shutoff is in case of a larger leak.
- Avoid chemical drain cleaners when you will be working on the trap or drain; they are hazardous and can make a small job dangerous.
Common Homeowner Questions
- Why do I get bubbles only sometimes? Often caused by intermittent air entry or partial venting; it can depend on how other fixtures are used.
- Can I fix a misaligned trap arm myself? Yes, if it’s simply loose or mis-sloped you can adjust it, but replace damaged parts or call a plumber if it’s cracked or corroded.
- Will adding water to the trap stop bubbling? It can help temporarily if the trap was dry, but if bubbling returns the underlying seal, slope, or venting should be checked.