I live in a 58 year old house built on a slab. My bathtub will fill with water when the shower is on. It will drain in a few minutes after you are done with shower. Meanwhile it fills about 2 inches or so, enough to cover your feet partially. I've put down some of the drain products you can get off the shelf in supermarket, and also home depot. This seems to clear the problem for about 3 days then it starts backing up again. I've been in this house for almost 5 years and its not gotten worse, it's always been the same routine, wait 3 days, pour some more stuff, etc. I've tried to use a snake and nothing comes out when I pull back the line. Its a mystery to me as to why this happens. Why would the drain cleaner work for only 3 days than we;re back to square one -

Oh and the bathroom is on the other side of the kitchen - so I think the pipe stand for the washing machine shares the same "exit" for the water from the tub.. could detergent suds and shampoo all be causing issues ? There is no problems ( thank God ) with the sinks in either room or with the toilet.

I have a small ranch 2 sinks - a washer, a toilet and a tub. All close to each other because the house is small, but the only nusiance is the slow tub. And the stand pipe for the washer also over flows from time to time with the rush of the rinse cycle.

I wish I had a basement to check for a clogged pipe but Im on a slab.