What type of drainage system relies on gravity to drain into the building sewer?

A Building Gravity Drainage System is the correct answer because it is designed specifically to rely on the force of gravity to facilitate the movement of wastewater from fixtures within a building to the main sewer line or building sewer. This system typically utilizes sloped pipes—installed at an angle—to promote efficient drainage by allowing gravity to pull the wastewater downward.

Gravity systems are vital for effective drainage because they do not require pumps or additional energy sources to move the water, which makes them more cost-effective and simpler to maintain. They are commonly employed in residential and commercial plumbing systems, taking advantage of natural gravitational forces to ensure that waste is removed efficiently.

In contrast, other types of drainage systems—such as the pressure, return, and suction systems—utilize mechanical components or pumps to move water, which is not applicable in a gravity drainage context. The pressure drainage system, for instance, would involve pumps creating pressure to transport wastewater, while suction and return systems also entail mechanisms that actively manipulate flow rather than relying on gravity alone.