Located on every roof top in every town, village, and city, is " the stink pipe. One of the largest contributors of toxic greenhouse gases and noxious sewer odors on the face of the earth. It is the source of that "awful smell" that gets into your house through air conditioners, vent fans, chimneys, open windows, etc.
Vent pipe filters are the solution to stink pipe odors,ie: Sweetfilter(tm)
Stink pipes pipes allow gas to escape from sewer mains and household plumbing so that water can flow down the drains.