Does it matter which way the P trap is position. I know it cannot be an S Trap but are there dos and donts regarding the direction after the trap. Im trying to fit a vent in the plumbing wall where my shower head copper runs and I was wondering if this will work or any other way I can turn the trap. I need to turn it because the bathtub drain is dead center of the no cut zone in the floor joists. You can see that I had to sister the old joists because the previous plumbers, probably when the house was built, cut in the wrong spots. Its 1 1/2" pipe and trap. There is 3" between the trap and the wye to prevent an S Trap. Thank you for you help.