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
howtomendit.com for free repair help, information and advice.
