What’s the Point of a Drain Trap?

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You may have seen the title of this article and wondered, never mind the purpose, what on earth is a drain trap? Drain traps are a functional component of the waste pipe coming from sinks, basins, bathtubs and toilets. Drain traps are an essential feature of almost all waste outlets leading to a drain. Even your porcelain toilet has one. Not very intriguing we know, but an essential nevertheless.

If you look under your kitchen sink or bathroom basin, you’ll notice the waste pipe has an S-bend or U-bend in it. This is the part of the waste pipe known as the drain trap. Some drain traps are external. Every single plumbing fixture directly connected to a sanitary disposal system must include a drain trap.

When purchasing plumbing fixtures for the home you will need to check what fittings they come with, and if you need to purchase extra fittings in order for them to be plumbed in. We would always recommend you use a reputable qualified plumber to fit anything with water pipes and drain traps to ensure the work is carried out appropriately.

You may of course need to purchase and replace a drain trap if you find a leak or if the essential seal is not working as it should. Bath drain traps often need to be replaced when a new bathtub is installed. Similarly, bottle traps are the type of drain traps that are fitted with sinks, so will likely need replacing when a new sink or basin is installed.

The purpose of a drain trap

A drain trap is designed to retain a small amount of water each time your sink, basin, bathtub or toilet drains. The standing water in a toilet is there because of a drain trap. The purpose of this is to create a seal and prevent sewer gas or odour, insects or vermin coming back into the home. This barrier is essential as sewage disposal systems and drains produce some pretty nasty odours. Common gases produced in a sewage system include:

  • Methane
  • Hydrogen Sulfide
  • Nitrogen
  • Carbon Monoxide

If there is a problem with any of the drain traps in your home it is essential you remedy the problem immediately. Sewage odours coming into the home pose significant health risks.

Additional benefits of drain traps

Lots of precious wedding rings and engagement rings have been saved by drain traps. Any small item that gets flushed down the plughole can potentially fall to rest in the bottom of the drain trap, so there’s an opportunity to get the valued item back.

The drain trap also collects hair and other detritus, limiting solid items going through to the rest of the plumbing.

Common problems with trap seals

There are occasions when a trap seal can be compromised. The most common reasons for this are:

  • Wind effect – you may notice when the weather is exceptionally windy that the water in your toilet bowl bobs up and down. The pressure or suction caused by strong winds can actually compromise the drain trap.
  • Evaporation – this is a common occurrence, especially for appliances with drain traps not in constant use. Holiday homes, remote floor drains, laundry room floor drains etc. can fall foul of water evaporation. Water from drain traps tends to evaporate if the trap isn’t used at least once a weak. Evaporation can compromise the seal.

 How to clean a drain trap

If your sink is draining slowly it’s probably due to a blockage. It’s not uncommon for hair and debris to build up in the drain trap. If you are unable to resolve the blockage using a sink plunger, you may need to simply clean out debris from the drain trap.

Another effective cleaning method to try if you prefer to err away from cleaning products full of chemicals is to pour baking soda and distilled white wine vinegar down the sink plughole.

If neither of the above cleaning methods are successful, you may need to remove and clean the drain trap.

How to replace a drain trap

It is possible to replace a drain trap yourself if you have sufficient DIY skills. However, it is prudent to employ an expert plumber if you aren’t confident in plumbing DIY.

Here’s an easy-to-follow YouTube clip to show how to replace a plastic sink drain trap.


As you can see, the humble drain trap has a very useful existence.

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