I have a Zanussi washing machine and dish washer that share a drainage pipe. The dish washer drains fine all the time. The washing machine drains so fast and with such high pressure that the water backs up the drainage pipe and spills out of it. I have had to put a large plastic box under the drainage pipe to catch this overspill and empty it at least twice a week. No doubt you will suggest trying to clear the drainage pipe, but dish washer is OK. What else to do ?