Vent, Valve & Volt
Sink drains slowly

You can fix this

Likely cause: a clog in the P-trap

With the stopper clean, the next stop is the U-shaped trap under the sink. Plunge first, then take the trap off and clean it out.

Why this happens

The P-trap is the U-shaped bend in the pipe under the sink. Bob Vila says it holds a small pool of water to keep sewer gas out of the house, and that it is also a prime spot for debris to collect. Family Handyman says to take the P-trap apart and clean it by hand if plunging has no effect.

How to fix it

  1. Has drain cleaner gone down this drain? Then do not plunge or open the trap. Lowe's says not to use plungers or other drain tools after a chemical drain cleaner. Call a plumber and say what you used.
  2. Plunge first. Bob Vila's method: use a cup-shaped sink plunger, block the sink's overflow hole with a small rag, add enough water to cover the plunger cup, and plunge up and down in short, quick strokes. Family Handyman says to expect splashing and wear rubber gloves and safety glasses.
  3. Optional, and only if no drain cleaner has gone down this drain: a baking soda and white vinegar flush for a slimy coating or a small clog. Bob Vila uses 1/2 cup of baking soda followed by 1/2 cup of white vinegar and waits 15 minutes. Home Depot uses 1/4 cup of baking soda and 1 1/4 cups of white vinegar and waits about 20 minutes. Rinse with hot tap water, not boiling water: Home Depot says boiling water can damage plastic pipes and porcelain sinks.
  4. Still slow? Bob Vila's first step for the trap is to turn off the water supply to the sink. Close the shutoff valves under the sink by hand. If one will not turn, do not force it. Leave it alone and keep the faucet off instead. Put a bucket under the trap, and make sure nobody runs the faucet while the trap is off.
  5. Loosen the slip nuts at both ends of the trap, turning them counterclockwise, and lower the trap. The water in it will drain into the bucket. Family Handyman says to loosen the joints gently so you do not crack or bend the trap.
  6. Push out the blockage with gloved fingers, a stiff brush or an unbent coat hanger. Those are Bob Vila's tools for it.
  7. Look the trap over. Family Handyman says to replace a trap that has cracks or weak walls.
  8. Put the trap back. Family Handyman's rule for slip nuts is hand-tight plus a quarter turn with pliers. Turn the water back on, run the faucet and check both nuts for drips.

When to stop. If a slip nut will not loosen without force, or the pipes look old or corroded, stop and call a plumber. If the trap was clear and the sink is still slow, the clog is farther down the line.

If this does not fix it, tell the plumber

  • Only this bathroom sink is slow, and the stopper is already clean.
  • You plunged it and took the P-trap off, and what you found inside.
  • Whether the trap or its nuts leak now.
  • Whether any drain cleaner went down this drain, and which one.

Build the full list: what to tell the plumber.

Start this troubleshooter over

References (every fact above comes from one of these pages)
  1. Bob Vila: How to fix a slow sink drain
  2. Family Handyman: How to clear clogged drains
  3. Family Handyman: How to clean and unclog a kitchen sink drain
  4. Lowe's: Unclog a sink, shower or tub drain
  5. The Home Depot: How to unclog a bathroom sink

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