Our shower never fully drains. The water remains standing about 12" down the drain. I am assuming this the trap. I've tried natural and chemical cleaners, and a 50' auger, but there was no change so I don't think this is blockage per se.
I've tried to fill the drain up further, but that seems to create just enough pressure to push some of the water through. It kind of acts like a toilet - the excess water swirls around the drain and at the end of it all I'm left with the same amount of water, not draining.
When I use a plunger, I hear the water drain further and at that point I can only see a little trickle at the very bottom of the pipe. So I think what's happening is that there isn't enough pressure from the the normal drainage process to push the water through the trap.
Any suggestions are welcome!