I have an old house around 80+ years old. It has a flat roof with a center drain that goes thru the whole house down to the basement to the sewar. This is not the problem pipe. Then I have another cast iron waste pipe that is directly underneath/connects to kitchen sink on first floor and kitchen sink on second floor. I've noticed that the wall inside the cabinets on the first floor is gets damp at times. When I hear the sink go glup glup I go to the basement and notice that water is leaking from the outside of the waste pipe onto the floor in my basement. The frustrating thing is that it does not happen all the time. HELP! Does anyone have any ideas/clues to the cause of this problem. I'd hate to have to tear into the kitchen cabinets and open the wall unless I have to. Like I said it does not happen all the time. but when it does, it leaks alot!