Wow... so many options, so many ideas. At this point after so many great solutions, unless there's an inherent concern with the concept I'm still leaning towards the vertical vent stack configuration per your design in post #27 appears. The only unknown (as far as implementing) is whether I plumb the tub using the partition wall as shown in #27 or go with the knee wall "variation" described in you most recent reply. Just to make sure I understand... in the recent reply, if I use the knee wall and bring the riser "through the floor" and eventually exit above the tub flood rim, I envision a vent loop per se. Correct... or am I confused? If correct... is there any problem with me then connecting the drain at the stack ?