When my washing machine drains it sometimes comes up and out of the open pvc pipe in the service closet where the water heater would drain. I've found lots of posts where people speak of the washer standpipe overflowing, but can't find any info on what would cause my problem. When the washer drains I have to stand at the service closet (next to each other in the garage) and watch/listen. First I can hear gurgling, then hear the water coming up the pipe (similar to the sound of filling a glass of water), then I can see the water just before it emerges and floods my service closet and garage. If I turn the washer off and on as it drains this doesn't happen...but not really feasible for the long run. Any ideas?