Final answer:
A waste pipe underneath a building is called a sewer line or sewage pipe, which is distinct from a siphon, as it provides a direct path for waste removal.
Step-by-step explanation:
The waste pipe underneath a building is typically referred to as a sewer line or sewage pipe. These pipes are crucial components of a building's plumbing system, designed to carry away waste water and materials from sinks, toilets, and other plumbing fixtures to a municipal sewage system or a septic tank. Unlike a siphon, which is a pipe used to convey water through an area that is higher or lower than the beginning and end of the siphon, a sewage pipe provides a direct path for waste to exit the building.