First question my guess is that there is a main drain pipe of sufficent diameter that it'll handle every toilet in the facility flushing at the same time.

Second question is that they are avoiding sewer gas that may come out of the drain if the unit is not used and it dries out.

I'm a facilities Tech, but I only have one floor and don't have any direct experience with high rise buildings.

I get a lot of smelly floor drains when the trap primers aren't working properly, which seems always the case with hard water out here.

Good luck with your google quest.