We remodeled a bathroom & I am finding conflicting info. Can a toilet & shower drain pipe run from 1st foor straight down through a cold air return (floor joists were panned)? Plumber did not drill hole in joist, the drain pipes run straight down and make their turns below the steel sheets (which are not in place).

Panning is not back up, and I am looking at this thing trying to figure out how I am going to re-pan the joists. All drain pipes have already been glued in... One of two things that has been giving me a headache.