The stub stack that my toilet waste goes into is leaking but only leaks water when it rains heavily outside??? I have cut out the breeze block at the base of the wall behind the toilet (in the garage)to see where the leak is coming from but the leak is coming from further up (inside ) the wall. I have a bathroom above this. I didnt think a soil pipe could be fitted onto a rainwater pipe? What should I do to sort out the problem?