I have a house built 1930. The pipe from the bathtub to the stack is clogged. Have tried drano, have used a Zip-it, have tried sucking out with a wet-dry vac. And it still does not drain, or does very, very slowly. Have poured hot water in the bathtub. You can feel the heat from this water is the pipes downstairs, and then you can feel where the water stops and the pipes are cold. How do you fix this?