Fix a Leaking Sink Trap: UK DIY Guide

By The FixDelivered Team · Updated 2026-07-05 · 7 min read

A leaking sink trap or waste pipe under your kitchen or bathroom basin can be an irritating nuisance, and if left unchecked, can lead to significant water damage, mould growth, and costly repairs. The good news is that many common sink trap leaks are straightforward to fix yourself with a few basic tools and a bit of patience. This guide will walk you through diagnosing the problem and carrying out the repair, specifically for a UK audience.

Why is my sink leaking under the basin?

Before you can fix the leak, you need to understand why it's happening. The most common culprits for a leaking sink trap or waste assembly include:

Loose connections: Over time, the nuts securing the trap components can loosen, allowing water to seep out.
Worn or perished seals: Rubber or plastic washers and O-rings can degrade, crack, or become displaced, losing their watertight seal.
Cracked or damaged pipework: The trap itself or connecting waste pipes can develop hairline cracks due to impact, age, or excessive tightening.
Blockages: A severe blockage can cause pressure build-up, leading to water backing up and leaking from weak points.
Incorrect assembly: If the trap was not installed correctly in the first place, leaks can occur from day one.

What type of sink trap do I have?

Understanding the type of trap will help you with disassembly and reassembly. In the UK, you'll most commonly find:

P-trap: Shaped like a 'P' on its side, these are the most common and connect horizontally to the waste pipe in the wall.
S-trap: Shaped like an 'S', these connect vertically downwards into the floor waste pipe. Less common in modern installations.
Bottle trap: A compact, cylindrical trap often used where space is limited, such as with pedestal basins.

Tools you'll need

Gathering your tools before you start will make the job much smoother:

Bucket or large bowl
Old towels or rags
Adjustable spanner or slip-joint pliers
Screwdriver (if your trap has jubilee clips or screws)
Wire brush or old toothbrush for cleaning
New rubber or plastic seals/washers (if replacing)
PTFE tape (plumber's tape)
New sink trap (if the old one is cracked)
Gloves and eye protection

Safety First

Before you begin, always prioritise safety:

Turn off the water supply: While a trap leak is usually on the waste side, it's good practice to turn off the main stopcock if you're unsure or if the leak is close to the supply lines.
Wear appropriate PPE: Gloves will protect your hands from grime and potentially harsh cleaning agents, and eye protection is wise for any DIY task.
Ventilate the area: Especially if dealing with stagnant water or using cleaning chemicals.
Never work on gas pipes: Any issues with gas appliances or pipework must ONLY be handled by a Gas Safe registered plumber.

Step-by-step Guide to Fixing a Leaking Sink Trap

Step 1: Preparation

Clear the area: Remove everything from under the sink to give yourself plenty of room to work.
Position your bucket: Place a bucket or large bowl directly under the trap to catch any water that will inevitably escape when you loosen connections. Lay down old towels for extra protection.

Step 2: Diagnose the Leak

Locate the source: Dry the entire trap and surrounding pipes thoroughly with a towel. Then, run a small amount of water down the sink and carefully observe where the leak originates. Pay close attention to all joints, nuts, and the body of the trap itself. You might need to gently touch the joints to feel for dampness.
Identify the type of leak: Is it a drip from a nut? A steady stream from a crack? Or is it only leaking when water fills the trap, suggesting a blockage?

Step 3: Repairing the Leak

Once you've identified the source, you can proceed with the repair.

If the leak is from a loose connection:

Tighten carefully: Using your adjustable spanner or pliers, gently tighten the leaking connection nut. Be careful not to overtighten, especially with plastic traps, as this can crack the plastic. Turn it just enough to feel resistance, then a quarter turn more.
Test: Run water down the sink and check for leaks. If it still leaks, proceed to the next step, as the seal might be compromised.

If the leak is from a worn or damaged seal:

Disassemble the trap: Place your bucket underneath. Using your spanner or pliers, carefully loosen the large nuts that hold the trap components together and to the sink waste and wall/floor pipe. Water will drain into the bucket.
Remove and inspect seals: Take apart the trap sections and remove all rubber or plastic washers and O-rings. Inspect them for cracks, hardening, flattening, or displacement.
Clean components: Use a wire brush or old toothbrush to thoroughly clean any grime, hair, or debris from inside the trap and around the sealing surfaces of the pipes and nuts. This is crucial for a good seal.
Replace seals: Install new, correctly sized seals. You can often buy universal seal kits or specific replacements from plumbing suppliers. Apply a thin layer of PTFE tape to the threads of plastic connections before reassembly, but ensure it doesn't interfere with the rubber seal itself.
Reassemble the trap: Carefully put the trap back together, ensuring all seals are correctly seated and not pinched. Hand-tighten the nuts first, then use your tools for a final gentle tightening. Remember not to overtighten.

If the leak is from a cracked pipe or trap body:

Replace the damaged part: If the trap body or a section of the waste pipe is visibly cracked, it will need to be replaced entirely. Take the old trap to a plumbing merchant to ensure you get a correctly sized replacement.
Install the new trap: Follow the reassembly steps above, ensuring all new seals are correctly fitted.

Step 4: Final Testing

Run water: Once everything is tightened, run water down the sink at a slow to medium flow. Carefully inspect all connections for any drips or seepage.
Increase flow: If there are no immediate leaks, run the tap at full flow for a minute or two, then fill the basin and let it drain completely. Continue to monitor for any signs of leakage.
Address remaining drips: If you spot a tiny drip, try a very slight additional tightening of the nearest nut. If it persists, you may need to disassemble, re-clean, and re-seat the seal.

When to call a professional

While many sink trap leaks are DIY-friendly, there are times when calling a professional plumber is the best course of action:

If you're unsure or uncomfortable: If at any point you feel out of your depth, it's safer to stop and call for help.
Persistent leaks: If you've tried the steps above and the leak persists, there might be a more complex underlying issue.
Complex pipework: If your waste system involves multiple connections, unusual fittings, or extends into walls/flooring, it might be best left to an expert.
Major water damage: If the leak has caused significant water damage, you'll need professional assessment and repair.
Emergency situations: For uncontrolled leaks or burst pipes, you need immediate professional assistance.

For persistent leaks or complex issues, it's always best to call a professional. At FixDelivered, we connect you with vetted local plumbers quickly. You can tell us your emergency and get help fast. Typically, a plumber's callout fee for a sink leak repair might range from £80-£150, plus parts, leading to a total cost of roughly £100-£250 depending on the specific issue, location, and time of day. Always confirm the price upfront with the plumber.

Preventing Future Leaks

Regular checks: Periodically inspect under your sink for any signs of dampness or loose connections.
Don't overtighten: When performing any plumbing work, remember that hand-tight plus a quarter turn with a tool is usually sufficient for plastic fittings.
Use strainers: A sink strainer can prevent food debris and hair from entering the trap and causing blockages or wear.
Avoid harsh chemicals: Strong drain cleaners can sometimes degrade plastic pipes and seals over time.

Fixing a leaking sink trap yourself can save you money and give you a great sense of accomplishment. However, if the task proves too challenging or the leak persists, don't hesitate to seek professional help. If you need a reliable plumber, remember you can find emergency plumbers near you through FixDelivered. Our booking fee is refundable if we can't find a plumber, and the plumber's callout fee is agreed directly with them upfront.

Frequently asked questions

How much does it cost to fix a leaking sink trap professionally in the UK?

As a rough guide for 2026, a plumber's callout fee for a sink leak might be £80-£150. With parts (which are typically inexpensive, £10-£30 for a new trap or seals) and labour, the total cost for a straightforward repair usually falls between £100-£250, depending on your location, the complexity of the issue, and the time of day.

Can I use silicone sealant to fix a leaking sink trap?

While silicone sealant might seem like a quick fix, it's generally not recommended for repairing a leaking sink trap. It's often a temporary solution that can mask a deeper problem, making future repairs more difficult. The best approach is to correctly identify the source of the leak (usually a loose connection or faulty seal) and replace the worn component or tighten the connection properly for a long-lasting, watertight seal.

How do I know if my sink trap needs replacing entirely?

You should consider replacing your sink trap if it has visible cracks or fractures in the plastic or metal body, if leaks persist even after cleaning and replacing all seals, or if the trap is very old and brittle. Sometimes, older, non-standard traps can be difficult to find replacement parts for, making a full replacement a more practical solution.

Need a plumber now? Tell us your emergency and FixDelivered will find and confirm an available local plumber near you, usually within the hour.

Written by the FixDelivered Team. Reviewed by Rupert Lowe, Editor. Last updated 2026-07-05.