Iím a DIY who remodeled a bathroom. In my shower, I had a joist directly below the hole in the pan and so I ran the drain 6Ē horizontal before turning down and into p-trap. From the P-trap I connected to toilet vent with a sanitary-T. The total distance from the drain to the connection to the toilet vent is about 3-4í including the trap. The toilet and tub (also connected to the toilet vent) drain well. Before I closed in the walls and for a few weeks afterward the shower drain worked fine. Now a few months later the drain is slow. The funny thing is that it is only slow until I hit it with a plunger. After that it drains well for the rest of the shower and any other showers for an hour or two later (Usually my wife). I canít understand why the slow drain keeps coming back? Iím pretty sure it isnít a clog (we havenít used the shower more than 100 times yet). Once I hit it with the plunger it drains really fast.
As I understand it, a santee can be used in the transition from horizontal to vertical, but not as a turn in the horizontal. Are you sure you have proper pitch to the line? Not having the trap directly under the drain means extra pipe that could get coated with crud and smell - not a great idea. It sounds like you tried to wet vent the shower...not a great idea, but possible if done right...it doesn't sound like yours is.
See what the pros have to say...
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013