Bathroom sink draining slowly? Clean the pop-up stopper and the P-trap

A bathroom sink slows down for one reason nearly every time: hair and soap scum wrapped around the pop-up stopper, with more of it settled in the P-trap below. Neither needs a plumber, and neither needs a bottle of anything. You need a bucket, an old toothbrush, a flashlight, and maybe a pair of pliers you will not have to use very hard.

Start at the pop-up stopper

The stopper is the metal or plastic plug in the drain opening. On most sinks it is held in place by a pivot rod under the sink: a horizontal rod that enters the back of the drain tailpiece through a nut, connected to the vertical lift rod behind the faucet by a flat strap and a spring clip. Some newer stoppers simply twist and lift out from above. If yours does, skip to cleaning.

1. Clear the cabinet and set the bucket under the drain.
2. Squeeze the spring clip and slide the flat strap off the pivot rod.
3. Unscrew the pivot nut by hand, or with pliers if it is tight, turning counterclockwise. Pull the rod straight out. A small plastic ball and a washer come with it; note their order.
4. Lift the stopper out from above. Expect a slug of hair and gray scum on the bottom half.
5. Clean the stopper with dish soap and the toothbrush. Scrub the drain opening and the overflow channel while you are there.
6. Run a zip-it strip down the drain. It is a flat plastic strip with barbs along the edge. Feed it in, twist, and pull. It brings back hair from the tailpiece the stopper could not reach. Do it three or four times.
7. Run hot water. If the sink drains fast now, reassemble. Push the pivot rod back through the eye at the base of the stopper, tighten the nut snug by hand plus a quarter turn, and refit the strap and clip. Adjust so the stopper seals with the lift rod up and opens fully with it down.

If it is still slow, take the P-trap apart

The P-trap is the U bend under the sink. It holds a plug of water that keeps sewer gas out of the bathroom, and it catches everything the stopper let through. Most are slip-joint: white PVC, black ABS, or chrome-plated brass, held together with two or three large nuts you can usually turn by hand, each with a washer inside.

1. Bucket under the trap. It holds a cup or two of water plus whatever is in it.
2. Loosen the nut at the top, where the trap meets the tailpiece, and the nut at the wall arm. Hand first. If they will not move, wrap the jaws of channel-lock pliers in a rag and go gently. Support the trap as the second nut comes off.
3. Drop the trap into the bucket and dump it out. Find the washers and note which way they face; the beveled side faces the joint.
4. Clean the trap with a bottle brush. Clean the tailpiece and look into the wall arm with a flashlight. A zip-it strip, or a coat hanger with the hook squashed flat, pulls hair from the first few inches.
5. Reassemble. Nut first, then washer, onto each pipe end before it goes into the joint. Hand tight plus a quarter turn. Plastic threads strip if you lean on pliers.
6. Leak check. Fill the sink, pull the stopper, and hold a dry paper towel against every joint while it drains. A drip means a washer is folded or a nut is cross-threaded. Take that joint apart and reseat it.

Chrome traps in older homes

Chrome-plated brass traps in homes from the 1960s through the 1980s corrode from the inside, especially along the bottom of the bend. One can look fine and feel solid, then crush in a wrench or crack at the bottom the first time it is disturbed. Green or white crust at the joints and pinholes on the underside are the warning. If yours is thin, replace it with a plastic slip-joint trap kit in the bathroom size, 1-1/4 inch, and match it to the tailpiece. If the drain stub coming out of the wall is also corroded, or crumbles when you touch it, stop there. That is a wall repair, not a trap swap.

Why chemical drain cleaners are a bad idea here

• They usually miss the clog. A hair clog sits at the stopper and the top of the tailpiece, above the water where the chemical settles.
• They eat the parts. Caustic and acid cleaners heat up and attack rubber slip-joint washers, corrode chrome brass, and pit the cast iron branch lines under the slab in homes built before about 1975.
• They wait for you. If the product fails, the trap is full of caustic water when you open it. Burns happen at exactly this step.
• They mix badly. Two products, or a cleaner and bleach, can make gas in a small cabinet.

Enzyme cleaners are harmless, slow, and fine for maintenance, but they will not clear a clog that is already there.

When a slow sink is not the sink’s fault

This is where cleaning stops and diagnosis starts.

• More than one fixture is slow. If the tub, the toilet, or the other sink has slowed down too, or the tub gurgles when the sink drains, the trap was never the problem. The branch line or the main is.
• The trap is clean and the sink is still slow. The clog is in the wall arm past your reach or in the branch line. That is a cable job, done from the wall arm or a cleanout.
• It drains fine, then slowly, then fine. A partial blockage downstream or a vent problem on the roof, and either one gets worse.
• Cast iron branch lines. In older homes the horizontal branch under the slab scales up until it is half its original size, and every fixture on it drains slowly no matter how clean the trap is. A camera finds it and tells you whether it is a cleaning or a repair.

If the stopper and trap were clean and the sink is still slow, or more than one drain in the house has slowed down, send us a note about what you found. It usually points to the branch line or the main, and a cable and a camera sort that out in one visit.