What is a building drain?

A building drain is specifically defined in plumbing codes as the part of the drainage system that collects waste from various fixtures within a building and conveys it to the building's sewer or other disposal system. This means the building drain is the horizontal pipe that receives all the wastewater from inside the building before it flows into the sewer line.

In this context, the correct answer emphasizes the function and location of the building drain as part of the overall drainage system. It serves to connect the interior plumbing fixtures to the exterior sewage system, encapsulating the role of the building drain in facilitating the flow of waste away from the building.

The other options do not accurately capture the definition of a building drain:

• Although sewage may be received by the building drain, it is the part of a drainage system specifically within the building, not just about receiving sewage.

• The connection to the main sewer typically refers to the building sewer, which is the part of the drainage system that extends from the building drain to the public sewer or septic system.

• A vertical pipe system is generally referred to as a stack or vent stack, which serves a different function in the plumbing system, focusing on venting and air circulation rather than waste transport.

By understanding these distinctions, one can see how the accurate