It's a "vented loop", and yes, it acts as vacuum break to prevent back siphoning (when functional, anyway).
04-07-2012 02:12 PM
I am replacing the original sewage lines in my Columbia and found this bronze elbow in the area behind the toilet. The sewage line goes up from the toilet to this elbow and then down to the sewage tank. At the top of the elbow there is this plastic screw in plug with a very small serated tip on the outside for a tube to attach to and a flap type end on the inside as per pictures. Can someone tell me what this is. When I removed it, it was completely plugged so I assume it wasn't working. Is this some kind of a vacuum relief valve. Any ideas. Thanks