How to unblock a bathroom sink: hair, pop-up wastes and traps

Bathroom basins rarely block all at once. They slow down over weeks. The water takes a little longer to drain after you brush your teeth, then a grey ring appears, then one morning the basin is still half full when you come back from getting dressed. That gradual pattern is good news. It usually means the blockage is close to the plug hole, within arm's reach, and made of things you can pull out with gloved fingers.

This guide works through the job in stages, from least effort to most. Stop as soon as the water runs freely.

What's actually in there

A basin blockage is nearly always a mix of three things:

• Hair. Long or short, it wraps around the plug mechanism and any rough edge it meets, then knits into a mesh.
• Soap scum. Bar soap reacts with the minerals in hard water to form a waxy deposit that coats the inside of the waste. Hair sticks to it very well.
• Everything else. Toothpaste, shaving foam and stubble, skincare products, cotton bud fibres and the occasional earring back.

Together they make a grey, slimy plug that smells worse than you'd expect. It collects in three places: around the pop-up plug, in the trap under the basin, and in the overflow channel. Kitchen sinks block for different reasons, mostly grease and food, and those are covered in what blocks a kitchen drain.

Before you start

Gather everything first, so you're not dripping across the house halfway through looking for a bucket.

• Rubber gloves
• A bucket or washing-up bowl that fits under the trap
• Two old towels: one for the floor, one for the cupboard base
• A plastic hair grabber (the cheap barbed strip) or a straightened wire coat hanger with a small hook bent into the end
• A cup plunger, the small flat-bottomed kind, not the toilet one with a flange
• A damp cloth to plug the overflow
• A torch
• An old toothbrush and a thin bottle brush
• Washing-up liquid

Empty the cupboard under the basin. Bottles stored in there have a talent for ending up in the bucket.

Stage 1: Lift out the plug and clean it

Most basins have one of two plug mechanisms.

Lever pop-up waste

This is the type with a small rod behind the tap that you pull up to close the plug. Under the basin, that rod connects to a horizontal pivot rod, which enters the back of the waste pipe and passes through a hole or slot in the bottom of the plug.

1. Look behind the waste pipe under the basin for the pivot rod and the small nut holding it in place.
2. Unscrew that nut by hand and draw the rod back a couple of centimetres. There's no need to pull it right out.
3. Lift the plug out from above.
4. Pull off the hair and slime. Expect a lot.
5. Drop the plug back in, make sure the pivot rod passes back through the hole in the plug's stem, then retighten the nut.

Check the plug opens and closes properly before moving on. If it won't drop, the rod has missed its slot.

Click-clack (push-button) plug

Press down to close, press again to open. With the plug in the open position, hold the body and unscrew the top cap anticlockwise. On some designs the whole plug unscrews from the waste. Clean it, check the small rubber seal, and screw it back.

Some older basins have a plain chain plug and a fixed grid. For those, skip to the hair grabber below and then Stage 2.

With the plug out, push a hair grabber down the waste, twist, and pull. If it comes back with a grey clump, repeat until it comes back clean. For many basins, the job ends here.

Stage 2: Plunge, with the overflow blocked

If the water still sits, try plunging. The overflow is the hole near the top of the basin, usually at the front or back. It joins the waste below the plug. If you don't block it, every push of the plunger sends air and water out through the overflow instead of down the pipe.

1. Push a damp cloth firmly into the overflow and hold it there, or ask someone to.
2. Make sure there's enough water in the basin to cover the plunger's cup. A few centimetres is plenty.
3. Seat the plunger over the plug hole and pump firmly ten or fifteen times without breaking the seal.
4. Lift off sharply and watch whether the water level drops.

Repeat two or three times. If nothing shifts, the blockage is further down, almost always in the trap.

Stage 3: Take the trap off

The trap is the bend under the basin that holds a little water to keep drain smells out of the room. It's also where heavier debris settles. Basins usually have one of two kinds.

Bottle trap

A cylinder hanging under the waste, often chrome on wall-hung basins or white plastic inside vanity units. The bottom section unscrews.

1. Put the bucket directly underneath and a towel around the base.
2. Unscrew the bottom cup by hand. If it's tight, wrap a cloth around it and use grips gently. Plastic threads strip easily.
3. Let the water and sludge drop into the bucket.
4. Pull out the inner dip tube if there is one, and clean both parts.

P-trap or U-bend

A curved pipe in a U or P shape, with a slip nut at each end.

1. Bucket underneath, towel down.
2. Unscrew both nuts by hand.
3. Lower the trap carefully. It's full of water.
4. Tip it out and look through it with the torch.

Cleaning and refitting

Wash the trap out somewhere else, in another sink or outside. Not in the basin you've just taken it off, which almost everyone does once. Scrub it with a bottle brush and washing-up liquid. Then shine the torch into the waste pipe going into the wall and clear whatever you can reach.

Before refitting, check the sealing washers. They should be flexible, not flattened or cracked. Refit hand-tight plus a small extra turn, run the tap hard for a minute, and put dry kitchen roll under each joint. A damp spot means a washer isn't seated properly.

Stage 4: Go further with a drain snake

If the trap was clean and the basin still drains slowly, the blockage is in the pipe beyond it, inside the wall or under the floor. With the trap off, feed a small hand-operated drain snake (a flexible auger a few metres long) into the waste pipe. Turn the handle as you push. When you feel resistance, keep turning: the spiral head either breaks through or catches the clog so you can draw it back.

Work slowly. Plastic waste pipe has tight bends and push-fit joints, and forcing a snake round them can knock a joint apart inside a wall. If the snake meets a hard stop, or the basin, bath and shower all drain slowly together, the problem is shared further along. The blocked drains guides cover what to check next, and toilets have their own method in how to unblock a toilet.

Enzyme cleaners or caustic?

Shop shelves offer two broad types of drain product.

• Enzyme and bacterial cleaners contain enzymes or live cultures that slowly digest organic material such as soap residue and skin cells. They're gentle on pipes and seals and work best as an overnight treatment for a drain that's sluggish, not stopped. They won't dissolve a hair mat.
• Caustic and acid cleaners work fast on organic matter, including hair. They're also hazardous to skin and eyes, can damage some older fittings and finishes, and make every later step riskier. If a caustic product doesn't clear the blockage, you're left taking apart a trap full of chemical.

If you use a chemical product at all: never mix two products, never plunge afterwards, and wear gloves and eye protection. For a bathroom basin, mechanical removal (plug out, trap off, hair grabber) is nearly always quicker and safer than either type.

Slow drain or bad smell? Different problems

A smell from a basin doesn't always mean a blockage. Work out which one you've got.

• Sour smell, water drains fine, seems to come from the overflow. The overflow channel collects a film of slime. Pour hot soapy water into it and scrub inside with a thin bottle brush.
• Sewer smell in a basin nobody uses. The trap has dried out, leaving an open path for drain gases. Run the tap for a minute. Spare bathrooms need this every few weeks.
• Gurgling when the bath or toilet empties, followed by a smell. Water rushing through the main pipe can pull water out of the basin's trap. That points to a ventilation problem, such as a stuck air admittance valve (a small cap-shaped valve on the pipework, often boxed in) or a blocked vent pipe. It's one for a plumber.
• Slow drain and a smell together. Usually the trap itself is dirty. Stage 3 sorts it.

Keeping it clear

• Fit a mesh strainer or hair catcher over the plug hole, especially if anyone in the house has long hair.
• Lift out the pop-up plug every month or two and wipe it. It takes two minutes and prevents most blockages.
• Once a month, run the hot tap at full flow for a couple of minutes with a squeeze of washing-up liquid. Use hot tap water, not a kettle: boiling water poured into plastic traps can soften or distort them.
• Brush hair over a bin, not over the basin.
• In a hard-water area, liquid soap usually leaves less scum than bar soap.

Quick answers

How long does it take to remove a trap? Around five minutes for a bottle trap, ten for a P-trap that has never been touched. If the nuts are seized or the plastic looks brittle, a replacement trap is inexpensive and fits most standard basin wastes.

Can I plunge a basin with a pop-up plug? Yes, but take the plug out first, or at least lock it fully open. Otherwise you're plunging against the plug.

Can I run the tap while the trap is off? No. Anything that goes down the plug hole lands on the cupboard floor. Put a note on the tap if anyone else is home.