HELP -- utility sink drained into my new washing machine!?

Question:We just moved into a new home. We were told that in order to drain our utility sink downstairs that we have to turn on a switch. When we did, the water just got sucked out of the sink. Today we had our washing machine hooked up. We painted today and rinsed out brushes and such in the sink and then put on the switch to drain the sink -- all the water went into my new washing machine.

Has anyone ever heard of a pipe with something like a "stopper" valve? Is it possible that my husband put in on upside-down? Is there a way to fix this problem? The delivery men wouldn't hook it up because they said it wasn't an approved hook-up for LG, but he said all we need was some clamp, etc. We bought exactly what he told us to and hooked it up. Now what??

Answers:
You can get a non return valve for the washing machine which would prevent this happening. It basically only lets the water flow one way. Meanwhile, try shaping the pipe in an 'n' shape behind the washing machine, with the top of the n higher than the utulity sink.
One more thing - if the washing machine does not have a filter, the valve is liable to clog, which prevents the machine from draining, it will just spin and spin and eventually give up. You would need to schedule a valve clean once a year or so.