Quick answer
A slow bathroom sink is almost always a hair-and-soap tangle wrapped around the pop-up drain stopper. Pull the pop-up up and out (or unscrew the retaining nut under the sink), pull off the hair mat, rinse, reinstall. Fifteen minutes, zero cost. If the sink is fully clogged and the pop-up is clean, the trap or the drain line has a clog — remove the P-trap and clean it (same process as the kitchen sink).
Key facts
| Common causes | Hair + soap scum on pop-up stopper; P-trap buildup; Branch drain clog |
|---|---|
| DIY difficulty | Easy |
| Time to fix | 15 min |
| Parts cost | $0–$10 parts |
| Tools needed | Rubber gloves, flashlight, drain snake (optional) |
| When to call a pro | If clog is past the trap |
What's happening
Every bathroom sink pop-up drain has a horizontal cross-bar or a mesh stopper. Hair catches on it, soap and toothpaste bind to the hair, and a dense mat builds up over months. The tangle sits right at the drain opening where it's easy to reach — but only if you know to pull the pop-up. Most homeowners try chemicals or plunging (both largely ineffective) and never think to look at the stopper mechanism itself.
Common causes (ranked by frequency)
- Hair + soap scum on pop-up stopper 80% of cases
The most common bathroom sink clog by a wide margin. Hair wraps around the stopper's cross bar; soap and toothpaste harden it into a felt. Pull the stopper and the mat comes with it.
- P-trap buildup 15%
If the pop-up is clean but the drain still runs slow, the trap has soap scum and hair buildup. Remove and clean (see fix #2).
- Branch drain clog 5%
Rare in bathrooms — usually only in older homes with narrow drain lines. Requires a hand snake.
How to diagnose
- Fill the sink partway. Slow drain suggests partial blockage; no drain suggests full blockage.
- Look down the drain with a flashlight. Often you can see the hair mat wrapped on the stopper cross bar.
- Try lifting the pop-up. Some pull straight out; others need to be turned or lifted off a pivot rod under the sink.
- If pop-up is clean and drain still won't clear, the clog is in the trap or drain line — proceed to Fix #2.
The fixes
Fix #1 — Clean the pop-up stopper 80% of clogs
Most pop-ups either lift straight out or require detaching a pivot rod under the sink. Both take 5 minutes.
Tools
- Rubber gloves
- Flashlight
- Old rag or paper towels
Materials
- Look under the sink. The pop-up has a pivot rod (horizontal metal arm) attached to the drain tailpiece with a nut and a small vertical strap.
- Unscrew the pivot rod nut (usually plastic) and pull the pivot rod out about an inch. This releases the pop-up.
- Lift the pop-up out from above. The hair mat comes with it.
- Rinse the pop-up thoroughly. Use paper towels to wipe off remaining scum.
- Reinsert the pop-up and reconnect the pivot rod. Test the lift lever — it should raise and lower the stopper freely.
- Run water for 30 seconds to confirm the drain runs fast.
Fix #2 — Clean the P-trap
Same process as the kitchen sink — but bathroom traps are usually smaller (1-1/4 inch) and easier to work with.
Tools
- Channel-lock pliers
- Bucket or bowl
- Rubber gloves
Materials
- Replacement slip washers (backup)
- Place bucket under the P-trap.
- Loosen both slip nuts by hand. Plastic traps almost always come off finger-tight.
- Slide the trap down. Empty and rinse.
- Reassemble hand-tight. Washers first, nuts snug — don't overtighten.
Prevention
Install a hair-catcher on the drain — a $3 mesh disc that sits over the drain opening and catches hair before it enters. Empty it weekly. Pull the pop-up and clean it every 6 months as preventive maintenance. Rinse the drain with hot water after each use to keep soap scum soft.
When to call a pro
When to stop and call a pro
- Pop-up is clean, trap is clean, drain still won't clear.
- Multiple bathroom fixtures drain slowly (sink + tub + toilet) — main branch issue.
- Sewer smell from the drain even when water is running — vent stack issue.
Bathroom drain service call: $120–$300. Multiple bathroom fixtures clogged suggests a shared branch drain issue, which runs $300–$600 for augering.
Cost estimate
Cost estimate
Frequently asked questions
No. Chemical drain cleaners can't dissolve the hair mat that's the real problem — they only soften soap scum. Physical removal via the pop-up is faster and reliably solves the issue.
There's a pivot rod under the sink connected to the pop-up. Unscrew the nut holding the pivot rod, pull it out an inch, then the pop-up lifts freely from above. Reversing the process reinstalls it.
Every 3–6 months for households with long hair; every 6–12 months otherwise. It's a 5-minute preventive task that stops the vast majority of bathroom clogs.
Very. A $3 mesh disc traps 95% of hair before it enters the drain. Empty into the trash weekly. Some homeowners find them visually unappealing — the alternative is more frequent pop-up cleaning.