I have a washing machine which is plumbed into the drain with a standard sort of appliance trap:


There's a nozzle for the appliance, an outlet connector which clamps onto the waste pipe, a P-trap, and a sink connector on the top.

The only thing is, i don't have a sink!

Well, not right next to the washing machine, at least. So currently, i have the sink connector open to the air. Most of the time, this is fine, but if the washing machine drains a particularly foamy load of water, then the foam shoots up out of the top, and spills all over the place.

Can i somehow seal the top of the trap? Is there a blanking plug which will fit this?

I had a look, but all the plugs i could find are for the connectors which joins to other bits of pipe, not the connector which joins to the sink, which seems to be different. The sink connector is a plain pipe with a threaded nut around it; the dimensions are:

  • Internal diameter of pipe 33.8 mm
  • External diameter of pipe 41.2 mm
  • Internal diameter of nut thread 45.5 mm

Is there something which will fit this?

2 Answers 2


Normally, in the absence of a laundry sink to route your drain to, a standpipe is used. There are pre-made standpipes available for purchase but I prefer to fashion my own out of larger diameter plastic pipe (PVC or ABS).

enter image description here

The standpipe is designed to hold the large volume of discharged water until it can drain down through the trap. Although there are devices you can buy to seal them up, I do not recommend it as drain siphon issues can come into play.

enter image description here

  • This makes a lot of sense. However, it's completely incompatible with the current layout in my kitchen! The P-trap clamps onto a waste pipe that is 700 mm from the floor, and which runs downhill along one wall to a point where it leaves the kitchen 600 mm above the floor. To use a standpipe, i think i'd need a waste pipe at about floor level, wouldn't it? Commented Nov 10, 2015 at 22:26

You should probably replace the trap with a washing machine trap

enter image description here

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.