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How to Fix a Leaking Sink Trap: A UK DIY Guide

By The FixDelivered Team · Updated 2026-07-04 · 6 min read

A drip, drip, drip under your sink can quickly turn from a minor annoyance into a major headache, potentially causing water damage, mould, and an unpleasant smell. Fortunately, many common sink leaks originate from the trap or waste pipe and can be fixed with a bit of DIY know-how. This guide will walk you through identifying the problem and carrying out the repair yourself, saving you time and money.

What Causes a Leaking Sink?

Before you dive in, understanding why your sink might be leaking can help you pinpoint the issue. Common culprits include:

• Loose Connections: Over time, the nuts and compression fittings on your sink trap and waste pipes can loosen, leading to drips.
• Worn or Damaged Washers/Seals: The rubber or plastic washers that create a watertight seal between pipe sections can degrade, crack, or become dislodged.
• Cracked Plastic or Corroded Metal: The trap itself or the connecting pipes can suffer from physical damage, especially older plastic traps or corroded metal ones.
• Blockages: A severe blockage can cause water to back up and put pressure on the trap, forcing water out through weak points.

Tools You'll Need

Most sink trap repairs require only a few basic tools:

• Bucket or large bowl (for catching water)
• Old towels or rags
• Adjustable spanner or pipe wrench
• Pliers (slip-joint or water pump)
• Screwdriver (if your trap has screws)
• New washers/seals (if replacing)
• Replacement trap (if necessary)
• Wire brush or old toothbrush (for cleaning)
• Plumber's tape (PTFE tape) or jointing compound (optional, for metal threads)

Safety First

Working under a sink is generally safe, but always keep these points in mind:

• Turn off the water: While not always strictly necessary for trap work, it's good practice, especially if you anticipate disconnecting the main waste.
• Electrical Safety: Be aware of any electrical sockets or appliances under the sink. Ensure they are dry and unplugged if there's any risk of water contact.
• Ventilation: If using any cleaning chemicals, ensure good ventilation.
• Gas Safety: If your leak is near any gas appliances (e.g., a boiler or gas hob), or you suspect the leak is related to a gas pipe (which is highly unlikely for a sink trap), never attempt to fix it yourself. Always call a Gas Safe registered engineer for any gas-related issues.

Step-by-Step Guide: Fixing a Leaking Sink Trap or Waste

1. Prepare Your Workspace

Clear out everything from under the sink. Place a bucket or large bowl directly beneath the sink trap to catch any water that will drain out. Lay down old towels to protect your cabinet base from spills.

2. Identify the Leak's Source

This is crucial. Run water into the sink and carefully observe the trap and waste pipes. Use a dry piece of tissue paper or toilet roll to dab around joints and connections. The tissue will absorb water, quickly revealing the exact point of the leak.

3. Tighten Connections

Often, a leak is simply due to a loose connection. Using your adjustable spanner or pliers, gently tighten the large plastic or metal nuts connecting the trap to the sink waste and the wall/floor waste pipe. Do not overtighten, especially with plastic fittings, as this can crack them. Test the leak again after tightening.

4. Inspect and Replace Washers/Seals

If tightening doesn't work, the washer or seal is likely the culprit. You'll need to remove the trap:

1. Place your bucket directly under the trap.
2. Unscrew the large nuts connecting the trap. There might be one at the top (connecting to the sink waste) and one at the side (connecting to the wall pipe), and possibly one at the bottom if it's a bottle trap.
3. Carefully remove the trap, allowing any standing water to drain into the bucket.
4. Inspect the washers (typically rubber or plastic O-rings or flat washers) inside the nuts and at the pipe connections. Look for cracks, hardening, or signs of wear.
5. If a washer is damaged, replace it with a new one of the exact same size and type. You can usually find these at hardware stores. Clean the seating surfaces where the washers sit before reassembling.
6. For metal threaded connections, you might also apply a thin layer of plumber's tape (PTFE tape) clockwise around the threads before re-tightening.
7. Reassemble the trap, ensuring all connections are hand-tight, then give them a quarter to half-turn with your spanner.

5. Check for Cracks or Damage

With the trap removed, inspect the plastic or metal body of the trap and the connecting pipes for any visible cracks, holes, or severe corrosion. If you find any, the component will need to be replaced. Take the damaged part to a hardware store to ensure you get an exact match.

6. Clear Blockages (If Applicable)

If you suspect a blockage contributed to the leak, or if you've noticed slow draining, now is a good time to clear it. With the trap removed, you can usually see and remove any hair, grease, or debris caught inside. A bottle brush or a bent coat hanger can be useful here. For blockages further down the waste pipe, you might need a plumbing snake or drain unblocker. Be cautious with chemical unblockers as they can sometimes damage pipes.

7. Test Your Repair

Once everything is reassembled, run water into the sink again, both a slow trickle and a full flow. Carefully inspect all connections and the trap body for any signs of dripping. If the leak persists, re-check each step or consider calling a professional.

When to Call a Professional Plumber

While many sink trap leaks are DIY-friendly, there are times when it's best to call in the experts:

• Persistent Leaks: If you've tried the steps above and the leak continues, there might be a more complex issue at play.
• Unidentifiable Source: If you can't pinpoint where the water is coming from, a plumber has specialist tools and experience to diagnose the problem quickly.
• Damage Beyond the Trap: If the leak is from the main waste pipe within the wall, or if the sink itself is cracked, professional help is essential.
• Lack of Confidence or Time: If you're not comfortable with DIY, or simply don't have the time, a plumber can resolve the issue efficiently.
• Gas Appliances Nearby: As reiterated, any issue potentially involving gas lines must be handled by a Gas Safe registered engineer.

For vetted local emergency plumbers, FixDelivered can connect you quickly. You agree the plumber's callout fee upfront, and our booking fee is refundable if no plumber is found, ensuring you get transparent service.

Preventative Measures

To avoid future leaks:

• Regular Checks: Periodically check under your sink for any signs of moisture.
• Avoid Harsh Chemicals: Strong drain cleaners can sometimes corrode or weaken plastic pipes and seals.
• Proper Disposal: Avoid pouring grease, coffee grounds, or large food particles down the sink, as these can cause blockages.
• Don't Overtighten: When cleaning or reassembling, hand-tighten plastic fittings first, then only a slight turn with tools.

Final Thoughts

Fixing a leaking sink trap or waste pipe is a common household repair that most competent adults can tackle. By following these steps, you can often resolve the issue yourself and prevent potential water damage to your home. Remember, dealing with a leaking sink promptly can save you from bigger problems down the line. Whether you fix it yourself or use a service like FixDelivered to find a reliable plumber, keeping your home leak-free is key.

Frequently asked questions

How much does it cost to fix a leaking sink?

If you fix a leaking sink trap yourself, the cost is typically just for replacement parts, such as new washers (a few quid) or a new trap (around £10-£30). If you call a professional plumber, they usually charge a callout fee, which can range from £60-£120, plus labour and parts. As a rough guide for 2026, a simple sink leak repair by a plumber might cost £100-£200, depending on your location and the complexity.

Can a leaking sink cause damage?

Yes, even a small, slow leak from a sink can cause significant damage over time. It can lead to warped cabinet bases, mould growth (which can be a health hazard), structural damage to flooring or walls, and attract pests. Addressing a leaking sink promptly is crucial to prevent these issues.

How do I stop a sink from leaking under the counter?

To stop a sink from leaking under the counter, first identify the exact source of the leak by running water and using tissue paper. Often, it's a loose connection or a worn washer on the sink trap or waste pipe. Tighten any loose nuts, or if necessary, remove the trap to inspect and replace damaged washers or the entire trap if it's cracked. If you're unsure or the leak persists, call a professional plumber.

What causes a sink trap to leak?

Sink traps commonly leak due to several reasons: loose compression fittings that connect the trap to the sink waste and wall pipe, degraded or cracked rubber/plastic washers and seals within these fittings, physical cracks or corrosion in the trap body itself (especially older plastic or metal traps), or blockages that cause water to back up and put pressure on weak points in the trap.

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