I have hooked up a single drain basin sink to the main line shared by our washing machine. The Washing machine now overflows out of the inlet and fills up the sink. How do I hook up the sink correctly to stop this. We used to have a double sink and did not have this issue. I really appreciate anyone's help!

You inatalled a sink downstream from your washer on the same branch? Is it on the same trap as the last sink? How close are the two? Why did you change sinks? What's different in your present vhookup from the last one? Back to you, Tom