I've lived in the house for 2 years and in the last few months have had problems with the dishwasher filling up with waste water. If the washing machine is switched on or the tap is run into the sink, the wast water can backup into the dishwasher.

I have cleaned out all the water traps and pipes so do not understand how this is happening.

I presume there should be some sort of on-way valve on the dishwasher waste to stop this happening?

Any advice?

Blue407, April 2012

Not all dishwashers have non return valves on the drain hose. As you have not told us what make & model dishwasher you have then I can't advise you on that. It sounds more like you still have a blockage somewhere down in the waste pipe or waste pipe is too small to cope with all the water at once from sink washing machine etc.

Lincoln Appliance NZ, April 2012

Normally dishwasher has non return valve but you can stop backflushing into it by raising the drain hose where it joins the sink plumbing so it comes from the fitting then goes right up beside the sink till it touches the underside of the worktop and tie it there so it cant fall down again this will form an anti syphon loop from the sink.

Kenjo, April 2012