My bath tub backs up. I have tried using a plunger and liquid drainer openers, nothing seems to work its only getting worst. My house is small and the plumbing lines seem to drain out together. What I mean is the kitchen sink is directly behind the bath tub or vice versa, and the toilet - when flushed affects the tub. This is not something that happens all the time only when the bath tub backs up, which is once every five year or so. Any suggestions? I know to call a plumber, are there any other potential problems I need to consider?