The most common cause of sewer gas smell is a dry water seal. Each drain contains a u-shaped pipe that traps a small amount of water to form a seal against sewer gasses rising into buildings. Drains that are seldom used can have this water evaporate over time allowing vapors to enter through the open piping. Pouring water down drains, including floor drains, can stop this problem. Non-toxic antifreeze, which is slower to evaporate, can also be used to vapor seal unused drains for longer periods. At time, sewer pipe venting located on a roof may become clogged or block (nests, bee hives, snow, etc) and this may cause sewer odor in a home or business.