Blocked Bathroom Sink? How to Unblock a Basin and When It's the Drain

If your bathroom sink is blocked, turn the tap off, check the overflow is not leaking, and look at what else in the house is draining badly. A basin that is blocked on its own is almost always hair and soap in the plug, the trap or the first half metre of pipe, and you can usually clear it in twenty minutes with a plunger and a bowl. If the basin fills up when the bath empties, when a toilet is flushed or when someone upstairs runs water, the blockage is in the shared pipe or the drain below, and that is a different job.

Why bathroom sinks block

Bathroom sinks block because hair, soap and toothpaste combine into a grey, stringy sludge that catches on the plug and the trap. Unlike a kitchen sink, fat is rarely the problem; hair is.

The waste pipe from a basin is narrow, usually 32mm, which is smaller than a kitchen or bath waste. Hair wraps round the stem of a pop-up or click-clack plug, soap binds it together, and toothpaste and shaving foam fill the gaps. Cotton buds, contact lenses, caps from toothpaste tubes and bits of broken soap are the usual objects we find in the trap. In hard-water areas, including most of London, scale also narrows old metal waste pipes over the years, so a small amount of hair is enough to stop them.

Is it the basin, the shared waste or the drain?

If only the basin is affected and the bath, shower and toilet all drain normally, the blockage is in the basin plug, trap or its own short waste pipe. If other fittings are slow, gurgle, or water rises in the basin when they are used, the blockage is further down.

Run the bath or shower for a minute and watch the basin. In many houses the basin waste joins the bath waste before both reach the soil pipe, so water rising in the basin while the bath empties means that shared section is blocked. Flush the toilet and watch again. Dirty water appearing in a ground-floor basin when a toilet upstairs is flushed points to the vertical soil pipe, and our guide to a blocked soil stack explains why the lowest fitting in the building is where it shows first. Finally, lift the nearest manhole cover outside. If it is full of standing water, the underground drain is blocked and nothing you do at the basin will help.

How to unblock a bathroom sink yourself

Start with the plug, then a plunger, then the trap. Most blocked basins clear at one of those three stages without any special tools.

• Take the plug out and clean it. A click-clack plug usually unscrews anticlockwise once it is in the up position. A pop-up plug with a lever behind the tap lifts out once the rod under the basin is loosened. Expect a clump of hair round the stem. This alone fixes a surprising number of slow basins.
• Plunge with the overflow blocked. Use a small cup plunger with a few centimetres of water in the bowl, and hold a wet cloth firmly over the overflow slot, or the pressure escapes through it. Twenty firm strokes, then lift off and watch.
• Clear the trap. Put a bowl under the basin and unscrew the bottom of the bottle trap, or the nuts on a U-bend, by hand. Empty it, rinse it and refit it hand-tight, then run the tap and check for drips. If the basin sits in a vanity unit, you may need to take the bottom shelf or back panel out to reach it.
• Pull hair from the pipe. A cheap barbed plastic drain strip, fed into the waste with the plug removed, will pull out hair from the first stretch of pipe that the plunger could not shift.

Use hot tap water, not a kettle straight off the boil, to flush the pipe once it is running. A ceramic basin holding cold water can crack if boiling water is poured into it, and hot water only softens soap; it does nothing to a clump of hair.

What not to do with a blocked basin

Do not pour a chemical unblocker into a basin full of standing water, and never mix it with bleach or another product. It sits in the bowl, it does not reach the hair, and it burns whoever takes the trap off next.

Avoid pushing a wire coat hanger hard down the plughole. On a pop-up waste it snags on the mechanism, and on older pipework it can push a clump of hair past the trap into the horizontal pipe, where it is harder to reach. Do not keep running the tap to see if it has cleared either; test with a jug of water so you can stop pouring the moment it starts to rise. If you have already used a chemical product, say so when you call anyone out.

Does a blocked bathroom sink need someone tonight?

Usually not. A basin that is blocked on its own, in a home with a working bath, shower or kitchen sink, can wait until the morning, and paying an evening or night rate for it is poor value. It becomes urgent when dirty water is coming up in the basin from other fittings, when the basin is overflowing onto the floor, or when several flats share the same pipe.

If the basin is overflowing because a tap will not turn off fully, close the isolation valve on the pipe under the basin. It is a small valve with a screw slot; turn the slot a quarter turn so it sits across the pipe. If there is no valve, turn off the stopcock. A single blocked basin is a job for a plumber in the daytime as much as for a drainage engineer, and our note on whether you need a plumber or a drainage engineer explains where the line falls.

Where the basin is only the symptom and the shared waste, soil pipe or underground drain is blocked, our drain clearance service clears it with rods or a jetting unit through the nearest access point. Our rates follow the clock: 7am to 5pm is the standard rate, 5pm to midnight the evening rate and midnight to 7am the night rate, with the current figures on our pricing page. The price is agreed on the phone before anyone travels.

Stopping the basin blocking again

A basin that blocks every few weeks needs less hair going down it, not more chemicals. Clean the plug every month or so, and fit a simple hair catcher if people wash or shave their hair over the basin.

Wipe excess toothpaste and shaving foam into the bin rather than rinsing large amounts away, and keep cotton buds, floss and cotton wool out of the plughole. If the basin still blocks regularly after the plug and trap have been cleaned properly, the waste pipe may have too little fall, a sag, or a heavy build-up of scale inside an old metal section. That is worth having looked at once it is clear, rather than plunging it every month.