The WPJ blog

In plumbing, a trap is a U-, S- or J-shaped pipe located below or within a plumbing fixture.

The U-bend is quite literally the deciding factor in whether your home smells of sewer gas or not, yet very few of us pay much attention to it at all. Today, let’s celebrate the U-bend and get to know it a little better.

A brief history

In 1880¹, Thomas Crapper introduced the U-shaped trap. Unlike its predecessor (the S-bend) it wasn’t prone to blocking and did not need an overflow.

The U-bend has been preventing sewer gases from entering buildings ever since. In refinery settings, it also prevents hydrocarbons and other dangerous gases from escaping outside through drains.

How does it work?

Due to its shape, a U-bend traps a small amount of water after each use. This water creates a seal that stops sewer gases passing back into the building.

An internal or external trap must feature in all plumbing fixtures, including sinks, bathtubs and toilets.

Maintenance

The beauty of the U-bend is that, despite being such an essential part of the home, it’s relatively low-maintenance.

With that said, the U-bend is the low point in most plumbing fixtures, so gravity can cause jewellery, hair and other debris to collect inside it. It’s for this reason that these traps can be disassembled or will incorporate a cleaning feature.

If the space allows for it, ask your plumber to make room for manoeuvre around the U-bend in your sink, just in case you do lose a ring down there.

It’s also worth noting that the water that acts as a seal inside the U-bend can evaporate if the appliance is unused for a sustained period of time, so do try to run water through your fixtures on a regular basis.

If you notice persistent draining problems, a more serious repair, replacement or maintenance service could be needed. Make a timeline of the issues and seek a professional plumber for guidance.