At an inspection today, I overheard two people speaking: One explaining to the other that the air-gap on the sink was an overflow for the dishwasher. She commented that, at her house, it always dribbles water back into the sink. This is the second or third time I have heard that conversation. Now I realize that most people do not know what the air-gap does. It looks like an oddity attached to the sink. Here is the deal. They are required, by most codes, for dishwashers and water softeners. The device, with no moving parts, is designed to eliminate a possible cross-connection between the potable water system and the sewage system. While not considered to be a large risk, without the air-gap there is always a possibility that unexpected discharge from the sewage system could siphon back into the drinking water. When these things spew, usually the hoses going to it or the device itself should be cleaned or replaced. Then again, if the hoses are reversed when the job is done, that can cause spewing too. In the realm of plumbing fittings, they cost little. The one below was an award winner in my book. I do not know if it was plumbed backwards or just plugged. At least the kitchen would not catch on fire when it was around and nobody needed a bucket to wash the floor.
Thanks for dropping by for a leak,
Steven L. Smith
Bellingham WA home inspector