I have a house built around 1953. The bath tub has a drum trap. I have had it snaked once by a plumber and it was a real mess. That was about 2 or 3 years ago. The drain ran fine for a while but now it runs slowly and every month or two I have to use the plunger on it or pour chemicals down the drain, which I would rather not do but sometimes that is all that works. I am wondering if it is a good idea to replace the drum trap with a p-trap and about how much it should cost for a plumber to do the job. How can I be sure it is the trap and not some other problem.