What is the term used for the lowest part of the plumbing system?

The term for the lowest part of the plumbing system is the building drain. This component functions as a crucial part of the drainage system, responsible for collecting waste and gray water from a building and directing it to either the public sewer system or a septic tank. Located below the fixture level, it connects the internal drainage system of the building to the external wastewater system, ensuring proper flow and preventing backflow.

The building drain serves as the pathway that allows gravity to work effectively, making it vital for the efficient functioning of the overall plumbing system. It is designed to carry away wastewater and is typically the primary conduit for waste materials once they leave the fixtures in the building. This makes understanding the role and function of the building drain essential for anyone involved in plumbing, particularly in maintaining and troubleshooting plumbing systems.