P traps are connected to drains with a slip joint into a threaded nipple that in turn goes into a tee. Considering the age of the house, the drain is very likely galvanized pipe and the nipple may be badly rusted on the end especially. The chrome pipes in the floor also a galvanized pipe and I would not consider them to be worth saving. They screw into pipes under the floor or in the wall. The hard thing about working on plumbing in an old house with galvanized pipe is finding a place to quit replacing pipe. Ideally, the whole house should be re piped, but that most likely far beyond what is in the budget for the bathroom renovation.