Quick Answer:

Water pools in the bowl and then slowly disappears because the drain is partially blocked or the drain assembly isn’t flowing freely. Start by inspecting the pop-up stopper, clearing the overflow slot, and checking the trap slope. Many cases are fixable with simple cleaning and a plunger; if water keeps backing up or smells like sewage, call a pro.

Why This Happens

Common causes are hair and soap scum building up under the pop-up stopper, a partially clogged P-trap, or a misaligned trap that doesn’t slope correctly toward the drain. The overflow channel can also be clogged so water bypasses the normal flow path and drains slowly. In some homes, poor venting or a larger clog down the line causes slow drainage too.

Step-by-Step What to Do

1. Inspect the pop-up stopper

Remove the stopper and look for hair, gunk, and mineral deposits. Many stoppers lift out or detach after you loosen a retaining nut or pull the pivot rod under the sink.

• Pull the stopper out and clean it with an old toothbrush or cloth.
• Use a flashlight to look into the tailpiece and the top of the trap for visible blockages.
• Reassemble and test the drain.

2. Clear the overflow slot

Clogs at the overflow can slow drainage. Run a bottle brush or a flexible brush through the overflow opening to dislodge hair and soap buildup.

• Insert the brush and scrub gently, then flush with hot water.
• If the overflow feeds into the drain assembly, cleaning it often improves flow noticeably.

3. Check and clean the P-trap

Place a bucket under the trap, loosen the slip nuts, and remove the trap to clear debris. This is where most hair and toothpaste collects.

• Empty the trap into the bucket, clean it, and run water through the pipes before reinstalling.
• Inspect the trap for damage or heavy mineral buildup and replace if needed.

4. Check trap slope

After reinstalling, make sure the drain pipes slope downward toward the wall drain without dips where water can pool. A short level or sight check will show if the trap slope is wrong.

• A trap that slopes upward toward the wall can slow draining — adjust pipe lengths or reposition the trap so it slopes gently down.

5. Test and escalate if needed

Run hot water and a few cycles of flushing with the stopper removed. If the drain improves, finish reassembling. If it still drains slowly, the clog may be farther down the line and need a plumber’s snake or professional service.

What Not to Do

• Do not overtighten plastic slip nuts — overtightening can crack the nut or strip threads, causing leaks.
• Don’t pour strong chemical drain cleaners into a partially blocked sink; they can damage pipes, harm you, and make professional work harder.
• Don’t force metal tools into plastic fittings; use the correct size wrench and support the pipes while you work.

When to Call a Professional

Call a plumber if:

• Water keeps backing up after cleaning the stopper and trap.
• Multiple fixtures are slow or the smell of sewage returns.
• There’s visible damage to pipes or you cannot access the clog safely.

For related issues that can point to a deeper problem, see Bathroom Sink Drips Only After You Turn It Off and Bathroom Sink Gurgles When Toilet Is Flushed for symptoms that often need a pro to diagnose.

Safety Notes

• Wear gloves and eye protection when working under the sink.
• Avoid mixing chemical drain products; if you’ve used them, ventilate the area and do not try metal tools without flushing the chemicals out first.
• Have a bucket and rags ready to catch water when you loosen fittings.

Common Homeowner Questions

• Why did this start suddenly? A small buildup finally blocked enough flow; sudden changes often follow hair or debris getting stuck at the pop-up or trap.
• Can I use a plunger? Yes — a cup plunger works well on sink drains after removing the overflow cover or sealing the overflow.
• Will vinegar and baking soda help? They can clear light soap scum but are not effective on heavy hair clogs; mechanical cleaning is usually required.