How do I connect a washing machine drain pipe to an undersink nipple?

ryanmalone

I'm struggling with a plumbing related problem ... how do I connect a washing machine drain pipe roughly 31mm to an under sink nipple roughly (very) 20mm.... the end of the drain pipe coming off the washing machine is hard and not rubbery so I don't think I could just clamp it on... also I've got to drill out the cabinet hole bigger unless the solution could be to attach it to a smaller hose first and then feed it through...🤔

Community manager's note: Check out How to connect a dishwasher for expert advice.

MitchellMc

Welcome to the Bunnings Workshop community @ryanmalone. It's wonderful to have you join us, and many thanks for your question about connecting a washing machine drain hose.

The simple solution would be to replace the hose on your machine with a conventionally sized drain hose, though you might also have an oversized fitting on the back of your machine. The issue with reducing the hose size to fit the barbed fitting is that your machine likely needs the larger hose to expel the water at its required rate. If you restrict that flow, you could inadvertently damage the pump.

Your hose is likely designed to be fed into an outlet on a sink as per the below image and not connected to the smaller barb under it. This setup has no restriction as it goes straight into the 40/50mm waste pipe. The barb on the S bend was initially designed for a dishwasher to hook up to as they pump out less water at a slower rate. Modern washing machines have now adopted this barb as their method of expelling water. Older top-load washing machines typically always go directly into the pipework via the outlet on the sink tub.

You are a bit stuck with the current setup, and it might be worth checking with a plumber to see if there are any options to have the pipe feed directly into the waste pipe rather than reducing the size of it to suit the barb.

Please let me know if you have any questions.

Mitchell