What is the name of the part of the drainage system that receives discharge from soil and waste pipes?

The component of the drainage system referred to in the question is known as the Building Drain. This part of the system plays a crucial role in collecting and conveying wastewater that has been discharged from soil and waste pipes. It essentially serves as the initial section of the drainage system within a building where these discharges are gathered before they move on to the main sewer line.

The Building Drain is designed to direct the flow of sewage and wastewater safely out of the building, preventing backflow and maintaining proper drainage. This strategic functionality is essential for keeping the plumbing system efficient and avoiding issues such as clogs or foul odors.

In contrast, the other choices represent different aspects of plumbing systems. The Main Sewer refers to the larger underground infrastructure that collects wastewater from multiple buildings and conveys it to treatment facilities. A Waste Stack is a vertical pipe that carries waste water and also includes additional components such as vents. Drainage Traps are critical for preventing gases from entering buildings by retaining a small amount of water, but they do not collect discharge in the way the Building Drain does. Thus, understanding the specific roles of each component helps clarify why the Building Drain is the correct answer for this question.