Originally Posted by gatorfan
The only place you should be using flexible pipe for a drain is when it's being pumped (e.g. dishwasher or clothes washing machine) and is accessible. All gravity drains should be rigid pipe. My guess is there's a clog in the flex pipe. It's probably smaller than code (a tub requires a 1.5" drain minimum, a shower 2") and the ridges will catch hair and other gunk.
I believe this may be the problem as well. Everyone of the ridges in the flex pipe, is probably full of gunk. I would get a few schedule 40 plumbing pipes, 2" or 1.5" - within code, and fix the flex pipe. It's really not too much work and a simple fix.
Have you poured any kind of compound down the drain to unclog it? I hear they are horrible for your pipes.