How to connect dishwasher and washing machine to one waste pipe

by Daniel Berry | Last Updated: 16/02/2021

I love my dishwasher, I have come to rely on it entirely, barley ever washing dishes in the sink. But when I moved home a couple of years ago I had a major problem upon moving into my new home. There was only one waste outlet on the under-sink waste pipe. I was stuck, it was either no clean clothes or back to the stone age and having to manually wash dishes in the sink.

Obviously, neither of these options was going to work for this lazy sod, so I took to searching for a workaround, and I can happily report that I found a few! There are two main ways to connect a dishwasher and washing machine to one waste pipe, one the proper way and the other the lazy mans way. Needless to say, I went the lazy way…

can you connect a dishwasher and washing machine to one waste pipe

can you connect a dishwasher and washing machine to one waste pipe

Connecting dishwasher and washing machine to one waste pipe

So like I said earlier you have two main options, I will talk through the pros and cons of both of these below.

Washing machine trap with double spigot

This is the proper, plumber approved, way of connecting your machinery to a single waste pipe. If you are lucky this will already be installed on your property. But as you have searched out this article using the power of Google then I can pretty confidently say you don’t already have one of these in your kitchen!

In fairness, this isn’t a hugely difficult job and if you are even remotely DIY competent you will be able to fit one. However, it can be dirty, depending on how old your existing U bend is it may well be full of slimly, foul-smelling gunk.

Also, depending on the arrangement of your under-sink cupboard it can be a very fiddly job. If you have plenty of room to get your hand and tools in and around your existing pipework this will be a straight forward job. If you don’t however it can get tricky and incredibly frustrating.

Just make sure you get the correct dimension trap for your existing plumbing. Note that most traps are a standard 40mm.

Sink Waste Trap with Double Spigot
£8.04

Quality polypropylene 40mm P Trap with x 2 appliance spigot. The trap uses easy-grip compression nuts, tapered rubber seal, rubber 'O' ring and a slip ring to give a secure watertight seal. The spigots give the option of attaching a washing machine and dishwasher. 

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03/06/2021 10:36 am GMT

Drain hose 3-way splitter

This is the simpler option and ultimately the option that I myself chose. You connect your two waste pipes to one which then feeds into the waste trap. I chose this simply because I cannot be arsed messing around with the U-bend under the sink.

This solution is more prone to failure and leaks but it is easier and quicker and can be done with just a simple flat-head screwdriver. This allows you to connect both dishwashers and washing machines to a single waste trap connection.

Drain Hose Y Piece Splitter Connector
£4.89
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03/06/2021 10:36 am GMT

FAQ’s

Can a dishwasher and washing machine use the same waste pipe?

Yes, I have been running my dishwasher and washing machine off the same waste pipe for over a year now with no problems. It has been used with both machines operating at the same time and again there were no problems.

How do you connect a dishwasher to a waste pipe?

The grey waste pipe needs to connect to your waste pipe. In the vast majority of cases, you will need to push the dishwasher waste (grey) pipe over a spigot under your sink. A spigot is a cone looking object with multiple steps on your U-bend pipe. You need to push the pipe over here as much as possible. Once it is connected you need to fasten it in place using a metal tie fastener. Add this to where the pipe connects to the spigot and then tighten it with a screwdriver. You want this to be tight but not overnight to the point it could be bending the spigot.

Do you need a plumber to connect a washing machine?

No, definitely not. This really is a job that anyone can do at home, even those normally averse to DIY. The water pipe will screw on to your water out. Nearly all pipes will have a valve where the pipe connects, you first turn this to the off position to stop the water flow. Then screw your water in pipe here, once it is connected you can turn the water back on. The waste pipe connects as I have shown in the question above.

Hey, I'm Dan, I studied computer science with artificial intelligence at Loughborough University. I try to bring my tech knowledge to the posts where it is needed while also offering a DIY view to go with Sam's professional view on tools. I am a very keen DIY'er and have experience of doing everything the completely wrong way.