My traditional colonial home was built in 1940. Galvanized pipes were used to plumb the upstairs bathroom. The bathroom is immediately above the main foyer. The bathroom is covered in old ceramic tile, which lays on concrete poured onto a subfloor. The tub drain uses a "drum trap," the outlet of which is imbedded in the concrete under the tile (to go across the bathroom floor to the toilet and main sanitary drain). I've had to replace the galvanized piping because of leaks and my plumber recommends changing the drum trap - requiring much more extensive demolition of the one and only bathroom in our house. I know that a p-trap should be used but, because of the construction, it's just not that easy. What should I do?