I'm not sure if this is a DIY issue, or if I need to call a plumber. The shower drains so slowly that the water backs up immediately upon turning on the water. But, if I turn off the water, let the water fully drain (very slowly), and then turn the shower water back on, it freely drains normally/quickly without any problem from that moment forward for that shower. Then, the next person who showers has the same problem---immediately on turning on the water, it drains so slowly that it backs up...but if they turn off the water, let it drain, and then turn the water back on, there's no problem, and it freely drains. I have put a snake down to find any hair, scum, etc., but there is minimal if anything down there. It's just odd, since simply turning the water off/on does the trick...but I have no idea why it's backing up the first time around for each shower. Thanks for any thoughts anyone has.

Showers and Bath Tubs traditionally have problems with hair in the drain. Particularly if anyone with long hair using the shower or tub. But your problem seems to be further down the line. So you need a 1/4" or larger snake (a 5/16" is better) that can be pushed through to the stoppage. The larger the snake the more difficult to get through the trap). The more turns the more difficult to traverse the line also. It may be further than you think. You need to understand the layout of your system to know how far to reach a 3" or 4" main line. Flush the heck out of it after you have gone through the stoppage as you pull the snake out. A cutting head is preferrable to a arrow head because the arrow may just push through and not clean to the diameter of the pipe. Go slow and be aware if you push too hard you could kink the snake and be in real trouble. Sometimes it is better to call an expert that has experience with clearing a pipe of debris.

Thanks....but why would it go extremely slow immediately, then work fine after it drains once---like clockwork, day in, day out? Why would you think that is a problem further down in the line? Wouldn't a blockage deep in the pipe consistently block the flow---not just the first time on each day?

couple of weeks ago there was a simolar problem posted. hj theorized (can't be sure if we aren't there) that there were 2 traps. the water didn't want to go thru the second trap. but, once it startred to flow thru it would drain normally.