What is a soil stack in plumbing terminology?

A soil stack refers specifically to a vertical pipe that is designed to carry human waste and contaminated water from fixtures such as toilets and sinks, down to the sewer or septic system. This pipe is crucial in the plumbing system, as it not only facilitates the removal of waste but also can integrate with the overall drainage system of a building.

In contrast, other options represent different aspects of plumbing. For instance, a pipe that carries freshwater does not fall under the category of a soil stack, as it pertains to potable water supply. Venting gases is important for the prevention of gas buildup in plumbing systems but is not the primary function of a soil stack. Lastly, while drainage is a part of the soil stack's function, describing it solely as a drainage pipe overlooks its primary role in waste transportation and the specific requirements related to sanitary systems.