I have a house that was built in the mid 70’s, it has a fiberglass tube and walls as a single unit.I would like to remove it and replace it with a steel tube. how can I disconnect the old drain pipe to install the new tube. The house has 2 bathrooms that share a common plumbing wall, but there is not enough room to get at the pipes via the walls. I will be redoing the walls with ceramic tile after replacing the tub. Any suggestion please let me know