I was doing some demo work in an unoccupied suite of an office building and noticed that a 2″ cast iron waste line from the suite above had been run through an existing Air conditioning duct.(kitchen sink) It appeared the length of pipe did not have any no hub couplings inside the actual duct…(it was a full 10’stick.) I guess it was cut through because of lack of grade to waste stack,ceiling height and the abundance of a/c ductwork in the way. Is this legal? I couldnt find anything about it in my old UPC book. Besides the obvious things like restriction of the air flow of the duct,possible failure of actual cast-iron and leakage of gas or waste into the duct, is there a section of the codes that specifically deals with penetration of duct work? Thanks, Learning.