Bath Waste Size (Plumbing)

This is a nice, short, and sweet article made just for you! Yes, Jim in Shaftesbury, we wrote it for you! Okay, I’m kidding… unless Jim is actually reading this. One way or another, we’re discussing bath waste size, specifically, how large the bath waste pipe should be. We’re going to talk about what the proper size is, why, and cover any other relevant bits before we wrap for the day. Now, onto the article!

The most common bath waste size for pipes is a 40 mm waste pipe. Sinks use a 32 mm waste pipe.

Now without further ado, let’s discuss it a bit more!

Properly Sizing Bath Waste Pipes

First things first – what is a bath waste pipe? In short, the waste pipe (sometimes called an overflow) is a secondary drainage hole. It’s designed to prevent overflow of the bath and gradually lower the water level. Now, sinks have these too, but their sizing is slightly different.

The primary reason for this is that showers and tubs have a much higher amount of water going through them at any given time than a sink will. Generally, a sink’s waste pipe will be 32 mm, while a bath waste pipe will be 40 mm to cope with the increased amount of water.

Keep in mind, however, that this is actually a guide rather than a rule. It really depends on when your home was built, and by whom.

On average, you’ll want to keep your waste pipe within a certain length range. If running it to a 110 mm branch, it’ll need to be within 3 metres of your shower or tub. If it’s a 50 mm branch, on the other hand, you’ll need it within 4 metres.

Final Thoughts

This was a nice, short, and easy article, huh? One question, one answer – just how we like it. To recap, your piping for bath waste size should be 40 mm. If it were a sink, it would be 32 mm, but you will rarely find a differently sized bath waste pipe. They’re generally universally sized unless the plumber who installed it really didn’t know what they were doing.

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About the Author Harry Thompson

Involved in home renovations throughout his life, Harry is an expert in everything to do with home and garden DIY. In his spare time, he enjoys cooking and tending to his garden.