I have constructed a floating boathouse in Ontario Canada. It is to have a small ,2 piece washroom in the cabin on top. (see pic). The lower part of the boathouse is completely open, much like a car port. There is to be a lav and wall mount toilet. The wall mount toilet was used so that there would be no plumbing visible from the lower deck. The waste stack travels down inside the center rear 6 x 6 steel tube column so 3 inch drain is not seen. The 3 inch waste stack continues down under the lower deck to the sewage ejection tank. From there the waste is pumped up to the septic tank on land. The problem is that the inspector insists that we need a 2 inch vent from the sewage tank travelling all the way back up inside the building and tied into the 3 inch stack exiting the roof. We cannot fit the 2 inch pipe inside the steel column now. We would have to leave the 2 inch vent exposed on the lower deck and run it up through the second floor. By code, could I run a separate 2 inch plastic abs vent inside a steel pipe, up the rear side of the building and carry on above the roof but not passing through the roof? I dont want to go through the roof and cedar shakes already installed. I would use this also as a flag pole , concealing the vent . any input is appreciated, thanks.