Is your sink leaking in the cupboard or all over the floor? If so, STOP, PUT YOUR PHONE DOWN, GO AND PUT THE PLUG IN THE SINK and PUT A BOWL UNDER WHERE THE LEAK IS! Have you done that? Good, now we can get started. It can be really frustrating when your U-bend leaks and literally millions of people experience this problem every year, and they usually have no idea what to do about it. This article will give you a few tips on how to stop the u-bend leaking under the sink so that you can get back to enjoying life without worrying about water damage!

U Bend Under Sink

What is a U-Bend?

A U-Bend is a ‘water trap’ or ‘trap’ for short. It is a U-shaped bend in the pipe that is designed to be filled with water creating an airtight water seal. Traps serve the important purpose of preventing any nasty gasses and odours from coming back up the system. These gasses are not only unpleasant to smell, but they also include highly combustible methane gas and a potentially toxic mix of other nasty chemicals.

There are a number of different variations on the trap, but they all have the basic ‘U’ part in their design as that is where the water sits – including a bottle trap that has the ‘U’ function hidden internally.

How to Stop Your U-Bend Leaking Under the Sink

A U-bend or kitchen waste leak is one of the easiest leaks to fix as the water is not under any real pressure and will only leak when water is run from the taps above. Anyone can fix a leaking u-bend using the following guide.

What You Need

As I said, this is an extremely easy leak to fix, and you do not really even need any tools. You will need a few things to ensure that the job gets done properly though and they are:

  • Kitchen Towel
  • Cloth/ Rag
  • Bucket
  • Gloves
  • New O-rings
  • New U-bend (If the old one is damaged or cracked)

Step 1 – Find the Leak

In order to stop a U-bend leak, you have to find which joint the water is leaking from. You can do this with a dry kitchen towel. Dry the area thoroughly and hold some kitchen towels around the joints of the U-bend. Then, run some water from the tap or open the plug hole and see which bits of the towel get wet first.

Knowing where the leak is will give you an idea of what parts you may need to fix it.

Step 2 – Try and Tighten the Nuts

Sink traps are held together by large plastic nuts. These nuts are also what are holding the seals in place. Check to see if these are loose before doing anything else. The nuts are usually just screwed on hand-tight so you should be able to see if they can be tightened and then run some water again to test. If it was as simple as that – Lucky You!

Step 3 – Remove the Trap

Okay, so if tightening the nuts has been unsuccessful, you will need to remove the trap. This is easily done by hand as the plastic nuts should come apart relatively easily. It may be a good idea to wear gloves for this bit. Make sure you still have your bucket or bowl in place and be prepared for the smell.

Not only does the trap fill with water to seal off the gasses, but it will also collect muck and debris that has gone down the sink and it does not smell nice at all!

Step 4 – Replace the O-Rings

Now, you may have a pack of spare O-rings in the shed and be lucky enough to have the exact ones you need but life is never that fair. You are likely to have to take a trip out to your local plumber’s merchant or B&Q to pick up the replacements. Make sure you take the old ones with you so you can buy like for like!

Step 5 – Put it All Back Together

It really is as simple as that unless the trap is actually damaged in some way, but this is easily replaced. When you are putting it back together, ensure that you are putting the O-rings in the correct place to ensure a nice and watertight seal.

Kitchen Sink U Bend
Kitchen Sink U Bend

Why Do U-Bends Leak?

Although O-rings can degrade over long periods of time, there are a few other reasons why u-bends tend to leak and most of them are avoidable if the right care is taken on installation.

Poorly Tightened Nuts

Yes, you would be surprised how many times the cause of u-bend leaking under a sink is caused by a failure to tighten the nuts up properly. A failure to tighten the nuts correctly means that the O-rings are not securely in place and therefore will not be creating the required seal to prevent the water from getting through.

Cross Threading

Another common occurrence with sink traps is that the threads are crossed, again, this leads to misalignment and the seals will not be held in place. Sink traps are made of plastic and therefore flexible. When tightening the nuts, there should not be too much resistance, if you have to force it too much, it may mean that you are cross-threading.

If you think this may be happening, undo the nut and start again.

O-Rings Have Moved

Yes, another common one that I have seen is where it has been obvious that the O-ring has moved during installation and has become bunched or bent into the wrong shape. Another instance where if you notice this, take it off and try again.


Although this one is a lot more uncommon, some O-rings have been known to wear and degrade over time. In this instance where you see worn, cracked or any other kind of damage, it is best to replace them immediately.

How to Stop U-Bends Leaking in the Future

The best way to prevent U-bends from leaking is to install them correctly. That means being careful when you have to periodically remove the trap for cleaning or if you are replacing an old one. I have known seals to degrade over long periods of time but if you notice any damage to one of the O-rings during routine maintenance, replace them ASAP.


As you can see, stopping a U-bend leaking under the sink is probably one of the easiest and least technical parts of plumbing that there is. It can be done at home on your own with no real tools necessary. All you need to do is ensure that when you are putting it back together, you are doing so carefully!

How to Fix a Leaky U-Bend Infographic

Plumbing Wizard Tips

“Remember that Installation is King. Get it right and your u-bend should not give you any more problems!”

“When you do any kind of maintenance on your trap, it is a good idea to ensure that all threads and seals are dry before reassembly!”

“Prepare for that smell when you take the trap off!”

“Before removing anything, check that the nuts have been tightened correctly – this may save you lots of unnecessary time-wasting!”

Frequently Asked Questions

How to unscrew the u-bend under the sink?

In most cases, these are made of plastic and can be undone by hand. Some are known to be made of metal and these may prove a little more difficult and appear seized. In this instance, use a wrench to undo the nuts.

How much does it cost to fix a leaking U-bend in the UK?

A new U-bend in the UK is under £10 and if you fit it yourself, this is all it will cost aside from your time. If you call in a plumber, however, this could become a lot more expensive depending on the callout charge.

How often should I replace my U-bend?

There isn’t a strict timeline, but if a U-bend is more than 10 years old and has recurrent issues or visible signs of wear and corrosion, it might be time to consider a replacement.

Are all sink traps the same size?

No, all sink traps are not the same size. Due to the variations in basin designs and the layout of the plumbing, there are variations on the simple trap too. There are bottle traps, s-bends, u-bends, j-bends, and all sorts of bends but they all ultimately do the same thing.

Is a leaking U-bend an emergency?

While a minor leak might not be an immediate emergency, it can lead to water damage, mould growth, or increased water bills if not addressed. It’s best to fix any leak as soon as possible.

Which basin trap do I need?

If you need to replace your trap, it is a good idea to get a like-for-like. If, however, you are looking to change your trap for some reason such as a new cupboard layout; sink traps need to be a minimum of 75mm deep and bath traps need to be at least 50mm.


Lee Pearce is not just a master plumber; he’s a veritable Plumbing Wizard. With over 30 years of experience in the trenches of pipes and drains, Lee has become the go-to sage for DIY plumbing, saving homeowners thousands in potential call-out charges. As the founder of Plumbing Wizard, he’s dedicated to demystifying the complexities of home plumbing, offering easy-to-follow advice that stands the test of time and pressure. His online blog is a treasure trove of tips, tricks, and tutorials that empower everyday individuals to take charge of their home’s plumbing health. Lee’s practical wisdom is not just about fixing leaks; it’s about imparting confidence and self-reliance. When he’s not writing or elbow-deep in a plumbing project, Lee is passionate about educating the next generation of DIYers, ensuring that practical skills are passed down and preserved.

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