Is it permissible to use a sanitary tee on it's back on a horizontal drain if it is solely for a dry vent only ( no waste ). The horizontal drain is on the second floor starting with the toilet, dry vent, then 2 fixtures downstream on wyes then down to basement (septic).
I would prefer the wye for the vent as well but it is a 3" stack and there is no room for the wye or combo even when rolling it. The stack continues to the roof. The sanitary tee is the red arrow in the pic.
If it is permissible does anyone know the UPC code to reference to?
Any advice appeciated...