Newbie question, probably: I recently took out my old fiberglass shower unit and replaced it with a tub. Problem is, the tub has never drained very quickly - about a gallon a minute, by my rough calculations.
Here's what I have tried so far:
- disassembled the P-trap and drained the tub directly into a bucket, through its drain/stopper/overflow assembly only. No problem, very fast.
- examined the P-trap for blockages. None.
- snaked the drain pipe leading away from the P-trap. No blockages.
- snaked the vent pipe on the roof. No blockages.

The only change I made to the old drain setup was to replace the old trap with a new one. OK, there's a possibility that the slope is slightly different. It's hard to measure how far it drops in the three feet of drain pipe that I can see, it's probably somewhere between 1/2 and 1 inch max.

Any ideas on what else I can try? Any ideas?