Quick Answer:
If the sink won’t hold water when the stopper is closed, it usually means the stopper assembly, a seal, or a downstream connection is leaking or venting air. Run targeted diagnostics to isolate whether the problem is the stopper linkage, the drain seals, the P-trap, a disposal or dishwasher connection, or a venting issue before attempting repairs.
Why This Happens
Water that disappears when the stopper is closed can escape in several ways: through a worn or misaligned stopper, a loose pivot rod or tailpiece nut, a leaking or clogged P-trap, or a connection to a garbage disposal or dishwasher that isn’t sealed. Poor venting can also create suction or gurgling that appears like a leak. For example, if you notice air noises or spurts, related problems such as Kitchen Sink Spits Air After Water Was Shut Off or Kitchen Sink Backs Up Only When Disposal Runs point to venting or disposal connections that need checking.
Step-by-Step What to Do
1. Confirm the symptom carefully
- Fill the sink to a known level, close the stopper, then watch for water loss over 5–10 minutes.
- Look under the cabinet for drips while the sink is full and after it has emptied.
2. Inspect the stopper and linkage
- Remove the stopper (many lift-and-turn or pop-up stoppers lift out after backing out the pivot rod) and look for cracks, mineral buildup, or missing gasket material.
- Operate the lift rod and pivot rod to confirm they move smoothly and seat the stopper fully.
3. Check the tailpiece and horizontal drain joints
- With the stopper removed, run water slowly and watch where it leaves the sink flange and tailpiece nut. Tighten hand-tight; then a slight additional turn with a wrench if the nut is loose.
- Replace any worn rubber washers or slip-joint washers if they look flattened or rotted.
4. Inspect the P-trap and disposal/dishwasher connections
- Place a bucket under the P-trap, remove it, and check for holes, gaps, or loose fittings. Reassemble with clean fittings and new washers if needed.
- If you have a disposal, check the knockout plug or the dishwasher inlet and the gasket where the disposal connects to the sink tailpiece.
5. Evaluate venting and air behavior
- Listen for gurgling when other fixtures are used; that may indicate a blocked vent or an AAV (air admittance valve) failure.
- Run targeted diagnostics such as filling one sink while running another and watching for changes in flow or air noises — this helps confirm a vent or shared-drain issue.
6. Test with the stopper reinstalled and retest
- After tightening or replacing seals, reassemble the stopper and linkage, fill the sink, close it, and time for leaks again.
- If the water level still drops but there are no visible leaks, the loss may be through a hidden defect or a venting/airflow path; note any odor or unusual sounds.
7. Record what you tried and what you observed
- Keep notes or photos of loose parts, replaced washers, and the exact behavior — this helps a pro diagnose faster if you call one.
What Not to Do
- Avoid forcing fittings — do not overtighten nuts or use excessive leverage. That can crack sink flanges or strip threads.
- Do not pour caustic drain chemicals into a sink that won’t hold water; they can damage seals, finish, and make later repairs hazardous.
- Do not ignore early warning signs like slow drainage, gurgling, or intermittent leaks — small issues often become larger and costlier if left alone.
When to Call a Professional
Call a plumber if you’ve checked the stopper, seals, P-trap, and disposal connections and the sink still won’t hold water or if you find corrosion, a cracked tailpiece, or a blocked vent. Also call if you detect sewage odor, persistent gurgling from vents, or if repairs require cutting plumbing or removing a disposal — these are best handled by a pro.
Safety Notes
- Turn off power to a garbage disposal before working on it.
- Wear gloves and eye protection when handling old seals or debris from drains.
- If you suspect sewer gas or see broken pipes, stop and call a professional; do not continue to run water or use household chemicals.
Common Homeowner Questions
- Why does the water level drop but there’s no visible leak?
Because the water may be escaping past the stopper or through a hidden joint, or air movement in the venting is causing suction that changes levels. - Can I fix a leaking stopper seal myself?
Yes — replacing the rubber washer or cleaning buildup often fixes it, but replace parts with correct-fit components and retest. - Will a disposal cause this problem?
Yes — a loose disposal inlet or a missing knockout plug can let water bypass the trap; inspect the disposal connection during diagnosis.