What is the term for the lowest horizontal piping of a drainage system that extends from the main stack?

The term for the lowest horizontal piping of a drainage system that extends from the main stack is referred to as the building drain. This component plays a critical role in a building's plumbing system as it collects wastewater from fixtures and conveys it to the building's sewer or septic system.

The building drain serves as the main conduit through which all drainage lines from sinks, toilets, and other fixtures flow. It is essential for ensuring that waste is properly managed and directed away from the building, thus preventing backflow and maintaining sanitary conditions. Understanding the function and terminology related to this part of the drainage system is crucial for plumbing professionals to ensure compliance with plumbing codes and standards, as well as to maintain the health and safety of plumbing systems.

In contrast, other terms listed may refer to components with different functions or locations within the plumbing system, which are not synonymous with the building drain.