Fix a leaking pipe under a sink
Save £60–120 in 30 mins — no plumber needed
A drip under the sink is usually a loose fitting or a failed rubber seal. Both take minutes to fix and cost almost nothing. This guide shows you exactly where to look and what to do.
Last updated: March 2026
Only basic tools needed — most homes already have them.
Before you start
This guide covers waste pipes under sinks — the grey or white plastic drainpipes that take water away from the basin to the wall. These are not under pressure; they only carry water when the tap is running or the basin is draining.
If the leak is from the small chrome pipes supplying the tap (the ones connected to the tap itself, under pressure), see our Fix a leaking pipe joint guide instead.
You do not need to turn off the water supply for this job unless you are replacing the waste outlet at the bottom of the basin.
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Tools & materials
- ✓Bucket or tray— to catch water when you undo the trap
- ✓Cloth or sponge— to dry pipework so you can see exactly where the drip is
- ✓Slip-joint pliers— only needed if the trap nut is too stiff to undo by hand
- !Replacement trap seal / washer— 32mm for basins, 40mm for kitchen sinks — buy a pack, they are pennies
- !Replacement bottle trap (if needed)— £5–15 at any plumbers' merchant or hardware shop
Want everything in one go?
Prices shown on retailer sites. Always check current pricing before purchasing.
Find the exact source of the leak
Put a bucket or tray under the pipework before you do anything else. Then run the tap slowly and watch closely. Most under-sink leaks come from one of three places: the connection at the plughole (where the waste pipe meets the basin), a joint between two sections of waste pipe, or the trap itself — the U-shaped or bottle-shaped fitting that holds water to block drain smells. Dry all the pipework with a towel, then run water again and watch for where the first drip appears. Why: you need to be certain which joint is leaking before you start loosening anything. Tightening the wrong joint wastes time and can disturb connections that were not leaking.
Most people get this done in under 5 minutes.
Where beginners go wrong
Not drying the pipes before testing. If the pipes are wet, you cannot tell where a new drip is coming from. Dry everything first, then run the tap.
Overtightening plastic trap nuts. The threads are plastic — they strip easily. Hand-tight is enough. If it still leaks after hand-tight, the issue is the seal, not the tightness.
Buying the wrong size replacement. Waste fittings come in 32mm (basins) and 40mm (sinks and baths). Take the old fitting with you when buying a replacement.
Tightening the wrong joint. Identify the exact source of the drip before touching anything. The drip point and the origin of the leak are sometimes different — a loose joint higher up can run down the pipe and drip from a lower point.
Stop and call a plumber if...
Water is leaking from the supply pipes to the tap — the thin pipes under pressure — not the waste pipes
The pipe in the wall is visibly cracked or the wall around the waste outlet is wet or stained
The basin itself is cracked around the waste outlet
The leak returns within a day of replacing the seal
Cost breakdown
Recommended starter kit
Five tools that cover most home repairs.
- →Adjustable spannerAmazon·Screwfix
- →Screwdriver setAmazon·Screwfix
- →PTFE tapeAmazon·Screwfix
- →Spirit levelAmazon·Screwfix
- →Tape measureAmazon·Screwfix
Want everything in one go? Get it on Amazon
What you just learned
You understand how under-sink waste plumbing is put together — the trap, the seals, and how to tell a supply pipe leak from a waste pipe leak. These skills transfer to replacing a full basin waste, fitting a new trap, and understanding waste runs throughout your home.
This unlocks:
⚠️ Watch out if you rent
Landlords are legally responsible for fixing leaking pipes. Report it in writing. If there is a risk of water damage and they do not respond within 24 hours, contact your council's Environmental Health department. Hand-tightening a loose waste pipe connection is generally considered acceptable emergency action for a tenant.