Recently, I discovered in my upstairs bathroom that water comes down from the toilet whenever you flush. I have taken out the toilet and actually poured water down the soil pipe and water comes down to the first floor. So, I believe that there is a crack somewhere in the soil pipe. The soil pipe is cast iron. I probably need to bust up the floor to get to the soil pipe…but..What type of material pvc, brass etc. should I get for my new soil pipe. What materials do I need to retrofit the cast iron and how should I amend it to the cast iron?