What defines the 'Building Drain' in a plumbing context?

The term 'Building Drain' refers to a crucial component of a plumbing system that is designed to carry wastewater and sewage from the interior of a building to either the public sewer system or a private sewage disposal system. It is called the 'building drain' because it serves as the main conduit that removes waste from all plumbing fixtures within the building.

Identifying the building drain as the lowest part of the drainage system is essential since it relies on gravity to effectively transport waste away from the fixtures and out of the building. This positioning ensures that any wastewater flows downward and prevents any backups or flooding within the structure. This orientation allows for efficient drainage and is critical for maintaining sanitary conditions within the plumbing system.

In contrast, the highest point in the drainage system would typically pertain to venting requirements or drain assembly design, while the access point for maintenance is not a defining characteristic of the building drain itself but rather a feature that might be incorporated in a plumbing system design for servicing or cleaning purposes. The connection of fixtures to the main sewer corresponds more closely with the function of branch lines rather than the definition of a building drain specifically.