So, you are saying if I use a San-Tee for the vent intake on a 45-degree angle off center that is acceptable, as long as the san-tee is not horizontal or vertical? So then I can use the san-tee on the outlet of the P-trap at a 45?
A san-tee is normally used like this: The through path is vertical, straight up and down. The trap arm comes into the side entry horizontally, the drainage goes out the bottom, and the vent comes off the top. So it's used to take off a vent while simultaneously having the drain turn downward.
What you can do it take that usual orientation and rotate it 45 degrees about the side entry, the trap arm. So if you were looking straight at the horizontal side entry, the top (vent) would be, say, up and to the left, and the bottom (drain) would then be down and to the right.
But if you're trying to minimize height loss as it sounds like you are, you'd surely be better off having the drain exit the vent takeoff on the horizontal. That requires the use of a wye or a combo (wye plus 45) for the vent take off, where the horizontal drain runs through the straight path of the fitting, and the side entry points up (or rolled up to 45 degrees from up).
And, another idea. Could I put the Street San-Tee on the outlet of the washer, and then attach the P-Trap on the spigot bottom of the tee, and then bring the vent in from the top of the tee? This will basically put the vent on the inlet side of the P-trap. Would this work?
Absolutely not, the vent goes after the trap, and as stated previously, for a 3" trap has to be 6" to 72" from the trap weir (the point water first spills out of the trap as it fills up).
Cheers, Wayne