Cleaning out a sink's P-trap yourself, step by step

What you need before you start

You do not need a large toolkit for this. An adjustable spanner or a pair of slip-joint pliers will loosen most trap nuts, though many modern plastic traps have wide plastic collars you can turn by hand or with gentle help from the pliers. Have a bucket or a wide, shallow basin ready, since the trap holds standing water and whatever has been sitting in it.

Old towels or rags on the floor are worth laying down before you touch anything, because water always finds a way past the bucket. A torch helps you see up into the cabinet, and a small bottle brush or a length of stiff wire is useful for scraping out the inside of the bend once it is open.

If the trap is old metal and the nuts have corroded solid, spray them with a penetrating oil and leave it fifteen minutes before you try to turn anything. Forcing a seized metal nut with pliers often rounds it off or cracks the fitting, which turns a five-minute job into a trip to buy a new trap.

• Adjustable spanner or slip-joint pliers
• Bucket or shallow basin
• Old towels or rags
• Torch
• Bottle brush or stiff wire
• Penetrating oil, for stiff metal fittings
• Spare rubber or fibre washers, just in case

The order for taking the trap apart

Clear out the cabinet under the sink and put the bucket directly beneath the trap before you loosen anything. Most kitchen and bathroom traps have two nuts: one where the trap meets the tailpiece coming down from the plughole, and one where it meets the horizontal pipe going into the wall or floor.

Loosen the lower nut first, by hand if it is plastic or with the spanner if it is metal, turning it anticlockwise. Keep one hand under the bend as it comes loose, because the water inside will drop the moment the joint opens, and it rarely lands neatly in the bucket on the first try.

Once the water has drained, work the second nut loose and lift the whole U-bend away. Set it in the bucket rather than on the towels, since whatever has been blocking it will usually slide out on its own at this point.

Clearing the bend and the drain behind it

Tip the trap out over the bucket and look at what has come out: hair and soap scum in a bathroom sink, food particles and grease in a kitchen one. Use the bottle brush or wire to scrub the inside of the bend, working it through from both ends until it comes out clean and the plastic or metal is visible again, not coated.

While the trap is off, shine the torch into the two open pipe stubs, the one coming down from the sink and the one going into the wall. It is common for a slow drain to be caused by build-up in these sections rather than in the trap itself, so poke the wire in a short way and check nothing else comes loose.

Rinse the trap under a tap or in a second basin until water runs through it freely with no resistance and no smell. This is also a good moment to check the rubber washers that sit inside each nut. If one is flattened, cracked or has lost its shape, it will not seal properly no matter how tightly you do the nut up, and it is worth replacing before you refit anything.

Putting it back together without a leak

Refit the washers in the same position they came from, then offer the trap back up to both pipe stubs before tightening either nut, so everything lines up without strain on the joints. Hand-tighten both nuts first, then give each a final quarter to half turn with the spanner or pliers.

This is the point where most people go wrong: overtightening. A trap nut only needs to compress the washer enough to seal it, and cranking it down hard tends to crack plastic threads or distort the washer so it leaks anyway. If it drips once the water is running, a small additional turn is usually enough, rather than starting over from full force.

Run the tap for a minute and check both joints and the tailpiece connection with a dry piece of kitchen roll pressed against them. Any dampness at all means the joint needs another small turn, or the washer needs replacing. Leave the cabinet door open for an hour afterwards and check again before you consider it done.

When to stop and call someone in

If the trap is clean but the sink still drains slowly, the blockage is further down the pipework than you can reach, and pushing wire or chemical cleaner further in rarely helps and can make things worse. This is a job for a plumber with proper rodding equipment rather than more force from your end.

Corroded metal traps that will not come apart without excessive force, cracked plastic fittings discovered once you are in there, or a smell that persists even with a spotless trap and full water seal, all point to a problem beyond a straightforward clean. Continuing to force fittings at that stage usually costs more to put right afterwards than calling in help would have.

Our plumbing service starts from 45 € per hour for exactly this kind of job, and general odd jobs from 39 € per hour cover smaller fixes around the same sink, such as a wobbly cabinet door or a tap that needs adjusting while the cupboard is already open.