Just moved into a new home and found that when my washing machine is draining water is coming up through sink, it only fills about one third of the sink, dont think there is a blockage because the water drains away quickly enough when you fill the sink and drain it, I know there is a rather long run on the waste pipe before it enters the main waste pipe and presume this has something to do with it. Is there any simple method of resolving this like a no return fitting that can be installed between sink and washing macine waste connector to stop back flow