In a building, which system is responsible for carrying sewage out to the public sewer?

The correct answer is the system that is primarily designed to transport wastewater, including sewage, from within a building to the public sewer system. Building drains serve this critical function by collecting waste from various plumbing fixtures and directing it through a network of pipes towards the main sewer line.

Building drains are typically situated beneath the floors of a building and are equipped to handle the flow of wastewater, ensuring it is properly channeled away from the structure to prevent any contamination or health hazards associated with sewage backflow. This system is essential for maintaining sanitation and hygiene in urban environments where buildings are connected to a municipal sewer system.

While ventilation pipes play a role in the overall plumbing system by allowing air to enter and exit drainage systems, they do not carry sewage. Similarly, building sewage systems and on-site sewage systems refer more to broader categories or methods of sewage management rather than the specific function of the pipes that transport sewage to the public sewer. Therefore, building drains are the designated systems responsible for this transportation, making them the correct choice in this context.