I have a basement drain that doesn't appear to have a "trap", at least as far as I can see. When I got close to drain to smell, it is awful. My old house I could always see water in it which I believe kept the sewage gas from coming back into the house. Should I be seeing water in this drain also? Could it have evaporated enough that the sewage gas could be coming up? Any suggestions beside dumping a gallon of water in it?