Q: The floor in our utility porch was recently ruined because the washing machine overflowed. We then moved the washer to the other side of the porch to allow better access to a utility sink, but its drain still overflows. We don't have this problem anywhere else in the house, which was built around 1924. Any hints on what to do?

— Mary, Ulysses, Kansas

A: Richard Trethewey replies: First have your plumber make sure there's nothing stopping up the washer drain. Then ask him to check the vent pipe or the soil stack — the one that sticks up through your roof — to see whether it's plugged by debris (like some unfortunate animal's carcass), and to make sure the washer's drain is connected to it. The vent equalizes air pressure so water can flow freely down the drain. Without it, overflows will occur whenever you drain a lot of water at once, which is exactly what washers do. (The same principle applies when you try to empty a soda bottle by tipping it upside down — the liquid glugs out slowly.) If neither the drain nor the vent is blocked, and the washer is properly connected to the vent, you probably have an undersize or corroded drain pipe. And even if they are in good shape, today's appliances pump out more water at a faster rate than old ones did, so it makes sense to bump up the size of the drain. If your washer feeds into a pipe that is now 1 ½ inches in diameter, for instance, increase it to 2 inches, all the way from the washer's drain back to the main waste pipe.
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