How to repair a leaking sink trap

How to repair a leaking sink trap

Jeremy, construction site supervisor, Cardiff

Guide written by:

Jeremy, construction site supervisor, Cardiff

131 guides

Does the base of your kitchen sink or wash basin flood each time you turn on the tap? Think the issue can be traced back to your waste trap? Never fear: we'll take you through a few handy tips to help you stop the leak and repair your leaky sink trap.

Important features

  • Identifying the location of the leak
  • Tightening the nuts
  • Removing the trap and replacing the seals
  • Checking the leak has been fixed
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The main causes of a leaking sink trap

In the plumbing world, a faulty sink trap constitutes a pretty minor leak.

The drainage system of your sink is kept under atmospheric pressure. The problem is therefore less serious than it would be if the leak was being caused by the pressurised water supply lines.

What's more, the waste trap is part of the drainage system meaning it will only leak when there is water running in the sink, unlike a leaky water inlet which will leak constantly. Here are the main reasons behind a leaky trap.

Poorly tightened parts

Plastic expands and contracts as temperatures fluctuate. If you haven't tightened the connections properly, parts of the trap may start to unscrew slightly as the plastic expands, causing the trap to drip. Check to see if you can tighten any nuts or screw couplings by hand.

Cross-threaded connections

The trap threads are made of plastic. Plastic is a flexible material which means that the threads may bend slightly and the joints may become cross-threaded. In this case, you simply need to unscrew the male and female connections and then screw them back together correctly, taking care to keep everything straight.

The O rings have moved

Sometimes when screwing two parts together, the O ring held between them can shift out of the correct position. If you suspect this has happened, simply unscrew the two parts and screw them back together making sure to check that the O ring is in the right place.

The O rings are worn or cracked

Over the years, rubber washers can wear out and start to break down. Unscrew your trap to check the condition of the O ring and replace it if necessary.

Faulty compression seal ring

The waste pipe is usually connected to the trap via a tapered compression seal which is used to keep everything watertight. If it is faulty, it will no longer be keep the system watertight and a leak will start. In this case, you will have to change the seal.

Steps

  1. Identifying the location of the leak
  2. Tightening the nuts
  3. Removing the trap and replacing the seals
  4. Checking the leak has been fixed

Required skills


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There's nothing too tricky about repairing a leaky waste trap. You don't require any technical skills; you simply need to be able to remove/install basic parts, detect a leak and replace seals.

Time required


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10 to 30 minutes

Number of people required


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1 person

Tools and equipment


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  • Water pump pliers
  • Cloths
  • Bucket or basin
  • Cutter

Personal protective equipment (PPE)


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  • Protective clothing
  • Pair of gloves
  • Safety goggles

Please note: this is a non-exhaustive list. Be sure to match your personal protective equipment to the job at hand.

1. Identifying the location of the leak


Leaky waste traps

To identify where the leak or drip is coming from, you can use an old plumber's trick which involves dipping your finger in powder and wiping it along each connection.

If the powder stays on your finger, there is no leak; if the powder is replaced by water, you have a leak on your hands.

This method allows you to identify even the smallest drips which may not be visible to the naked eye.

2. Tightening the nuts


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Your leak may simply be caused by a slightly loose screw coupling.

  • Try to tighten the connections around the source of the leak by hand.
  • Run the water to check if the problem has been resolved.

3. Removing the trap and replacing the seals

Replacing the O rings


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If the issue hasn't been fixed, you will need to remove the trap.

  • Place a bucket under the trap to collect the water stored inside.
  • Unscrew the trap by hand or using a pair of water pump pliers if necessary (placing a cloth over the screw couplings so as not to damage the plastic).
  • Clean all parts from the tailpiece down to the waste pipe.
  • Remove the faulty rubber O ring and replace it with a new one.
  • Reassemble the various parts and connect the waste back up to the base of the plug and the drain pipe.

Replacing a tapered compression seal


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If your leak is located around the drain pipe, the problem is with your compression seal.

  • Unscrew the coupling nut from the drain pipe.
  • Check the condition of the seal and throw it away if damaged.
  • Clean everything.
  • Put the screw cap in place then insert the compression seal linking the trap to the drain pipe.
  • Tighten the screw cap around the pipe.

4. Checking the leak has been fixed


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Run the water in your wash basin or sink and repeat the finger test described above to ensure that the leak has been resolved.

If everything looks good, then congratulations! You've just repaired your leaky sink trap.

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Guide written by:

Jeremy, construction site supervisor, Cardiff, 131 guides

Jeremy, construction site supervisor, Cardiff

Electrician by trade, I first worked in industrial estates where I installed, wired and fixed a large number of electrical installations. After this, I managed a team of electricians for this type of work. 10 years or so ago, I turned to building and construction. From the modest family home, to gyms and theatres; I have been able to coordinate, audit and organise all sorts of construction sites. for 4 years now, I am restaoring and bulding an extrension to a bungalow in the heart of the welsh countyside. My experience in manual work and my knowledge means I am proud to be of service. Terraces, interior design, roofing, plumbing, electricty, anything goes! We have, my wife, daughter and I, built almost everything we have from scratch! So to answer all of your questions, and to orientate and advise you on coosing your tools? Easy!

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