The main soil stack is a portion of a home’s plumbing system that connects to the interior plumbing to the sewer itself. These pipes are found in various types of buildings. When the system uses this soil stack, a pipe runs vertically from below a building to a vent found on the roof. When waste water leaves a sink, bathtub or toilet, it flows through a waste water pipe to a soil stack. These pipes are typically slanted downwards to assist in the waste removal. Once this water hits the soil stack, the materials travel down and the gases travel up. At the bottom of the soil stack, the materials exit the waste-removal system. This will go to a sewer in urban areas or septic tanks in rural areas. This is a neutral pressure system where the air pressure within these pipes is the same as the air pressure outside of it. This creates a suction effect, which helps to prevent blockages.