sewer gas
More properly sewer air. The contaminated air of sewers, house drains, soil, waste, and vent pipes. It is a mechanical, ever-varying mixture with common air of a number of gases due to the decomposition of animal and vegetable matter, such as carbonic dioxide, carbonic oxide, ammonia, carbonate and sulphide of ammonia, sulphuretted hydrogen, and marsh gas. Sewer air also contains organic vapors, and some microscopic germs or bacteria. (Sturgis, 1900)