Our house is on a slab and the washer drain is a 2 inch copper pipe that was probably big enough in FREAKING 1958. Well 50 years later, it sucks and there isn't much we can do about it except keep the pipe squeaky clean with a plumber's snake. We generally have it snaked once or twice a year, but we are obviously overdue.
So I had a brilliant idea, pull the fridge back out and get 2 buckets and the next time the washer drained, take turns filling the buckets and dumping them in the sink. Whoda thunk a washer could drain 2 gallons of water faster than I could dump it in the sink. It wasn't too bad at first, but it just kept draining and draining, and with each bucket, about a quart of soapy water sloshed out onto the carpet - about 10 times. Not to mention the rapidly nervous dumping sink water mess. Bring out the shop vac again and turn on the fans and call the plumber. Did I mention I smacked my head on the kitchen cabinet? No stitches, but I saw stars for about an hour..
Yes, it could have been much worse if it had slowly leaked over a longer period, but I have had enough already. So along with the checklist from my last post, check your washer drain while I go get drunk.