Which system is responsible for managing sewage and drainage inside a building?

The Building Drainage System is specifically designed to handle sewage and drainage within a building. This system is essential for the proper disposal of wastewater, ensuring that it can flow freely from fixtures like sinks, toilets, and showers to the main sewer line or to an on-site sewage treatment system. It includes all piping, fittings, and fixtures that facilitate this process, making it crucial for maintaining hygiene and sanitation inside the building.

While the Building Plumbing System encompasses a broader range of functions, including the supply of potable water, the management of sewage is distinctly within the purview of the drainage system. The Building Venting System is responsible for allowing gases to escape and maintaining proper pressure within the drainage system, but it does not directly manage sewage or drainage. Finally, the Building Isolation System is not a recognized term within plumbing codes and does not relate to sewage management. Thus, the emphasis on the drainage system's role in effectively managing waste flow makes it the correct choice for this question.