detached two storey house. when the second floor bathtub is used water is leaking onto the basement ceiling as it clings on to the outside of the drain pipe and leaves it as the drain pipe makes a 90degree turn at the basement ceiling. when the sink in the same second floor bathroom is used, there are no leaks. when the main floor laundry room is used, there are no leaks. what’s strange is they are all on the same drain line. how is it that only using the bathtub causes a leak and nothing else?