How to Change a Sink Trap Without Causing Leaks
A leaking sink trap is one of the most common plumbing problems in UK homes. Fortunately, replacing a trap is usually a straightforward job — but it’s also one that regularly goes wrong because of poor fitting, damaged seals, or incorrect alignment.
The biggest issue people run into is leaks after installation. In most cases, that comes down to the washers and seals being fitted incorrectly rather than the trap itself.
In this guide, we’ll explain how to change a sink trap properly, the most common mistakes to avoid, and when a small leak could actually point to a larger drainage problem.
What Does a Sink Trap Do?
The trap is the curved section of pipe underneath your sink that holds a small amount of water. This water creates a seal that stops unpleasant drain odours from coming back up through the pipework.
Most kitchen and bathroom sinks in the UK use either:
A bottle trap
A P-trap
A flexible waste trap
Over time, these can start leaking due to:
Worn seals
Cracked plastic
Loose compression fittings
Misaligned pipework
Blockages causing pressure issues
Tools You’ll Need
Before starting, gather:
Adjustable grips or pipe pliers
A bucket or bowl
Old towels or cloths
Replacement trap kit
New compression washers (usually included)
Gloves
You generally won’t need sealant or PTFE tape for a standard trap replacement if the seals are fitted correctly.
Step 1: Remove the Old Sink Trap
Start by placing a bucket underneath the trap to catch any water.
Most modern traps use hand-tightened compression fittings. Unscrew these carefully and lower the trap away from the waste pipe.
If the fittings are stiff:
Avoid overtightening with grips
Support the pipework while loosening
Check whether previous installers have used unnecessary sealant
Once removed, inspect the old trap carefully. Cracks around threaded joints are extremely common.
Step 2: Check the Waste Pipe Alignment
One of the biggest causes of leaking traps is pipework that doesn’t line up properly.
The trap should sit naturally between:
The sink waste outlet
The waste pipe entering the wall
If you have to force the trap into position, the seals will often fail over time.
Cheap flexible traps are frequently used to compensate for poor alignment, but they can create long-term reliability issues if stretched or twisted excessively.
Step 3: Fit the New Seals Correctly
This is where most people get caught out.
Compression washers only seal properly when fitted in the correct direction. The tapered edge should normally face towards the fitting.
Common mistakes include:
Installing the washer backwards
Reusing old seals
Overtightening the fittings
Forgetting a washer entirely
Cross-threading the nut
Overtightening is particularly common. Plastic traps only need to be firm hand-tight. Excess force can distort the washer and actually create leaks.
If a fitting continues leaking after tightening, don’t just tighten it further. Take it apart and check:
Washer orientation
Pipe alignment
Dirt or debris on the sealing surface
Step 4: Reassemble the Trap
Once the seals are in place:
Connect the trap to the sink waste
Connect the outlet pipe to the waste pipe
Tighten all compression nuts evenly
The trap should sit comfortably without strain on any joints.
Avoid using silicone or adhesives around compression fittings. A properly fitted trap should seal without them.
Step 5: Test for Leaks Properly
Run water through the sink for several minutes while checking every joint carefully.
A good trick is to dry all fittings with tissue paper first. Even small drips will show immediately.
Also check:
Around the basin waste itself
The rear waste pipe connection
Any threaded sections underneath the sink
Sometimes what appears to be a trap leak is actually coming from the sink waste above it.
When a Small Leak Could Be a Bigger Drainage Problem
In some cases, recurring leaks or smells underneath a sink may point to a wider drainage issue rather than just a faulty trap.
Problems such as:
Partial blockages
Poor waste pipe installation
Backflow issues
Incorrect pipe gradients
can all put extra stress on sink waste fittings.
This is especially common in rental properties and older buildings where pipework has been altered multiple times over the years.
How Much Should Sink Trap Replacement Cost in the UK?
For a straightforward replacement, most plumbers in the UK would typically charge:
£60–£120 for labour
Plus the cost of the trap itself
Costs may increase if:
Pipework needs modifying
Access is difficult
Additional leaks are discovered
The basin waste also needs replacing
If you receive a surprisingly high plumbing or drainage quote, it’s worth getting a second opinion before approving the work.
Drain Quote Check helps homeowners, landlords, and property managers review drainage and plumbing quotations so they can better understand whether the recommended work — and pricing — is reasonable.
FAQs
Why is my sink trap leaking after replacement?
The most common causes are incorrectly fitted seals, overtightened compression fittings, or pipe misalignment.
Can you reuse sink trap washers?
It’s always better to fit new washers when replacing a trap. Old seals can harden or deform over time.
Should sink trap fittings be hand tight?
Yes. Most plastic compression fittings only require firm hand tightening.
Do I need a plumber to replace a sink trap?
Many people can replace a trap themselves, but recurring leaks or drainage smells may indicate a larger issue that needs professional investigation.
Final Thoughts
Changing a sink trap is usually a manageable DIY job, but the small details matter. Correct seal installation, proper alignment, and avoiding overtightening make the difference between a long-lasting repair and a persistent leak.
And if you’ve received a plumbing or drainage quote that doesn’t feel right, getting an independent review can provide peace of mind before committing to the work.
Not Sure Whether Your Quote Is Fair?
Drainage and plumbing quotations can vary significantly, making it difficult to know whether you're paying the right price for the right work.
Drain Quote Check independently reviews quotations and reports, helping homeowners, landlords, and property managers understand exactly what they're being charged for and whether the recommended work appears reasonable.
Before you spend hundreds or even thousands of pounds, get a second opinion from a drainage specialist.
