A girl friend of mine called to say her washing machine drainage had shot back into the house. I went to check the problem. Her house is on pillars and the drain's pee trap was under the house... the water in it had frozen, blocking the drainage. When her washing machine tried to drain, the only place for the water to go was back into the house.
Melting the frozen water, with a hair dryer, under the house was the solution.... until the next time. Location: Lafayette, LA