Illinois State Plumbing Practice Exam

In a drainage vent system, the function is to let air into the system to prevent trap siphon as wastewater flows. The pipe that connects one or more individual fixture vents to the larger vent stack is called a branch vent. It serves as the connecting segment that ties individual fixture vents into the main vent line that runs to the roof. A roof vent is simply the opening through the roof for the vent stack, not the connector from the fixture vents. A main vent describes the larger vertical line that serves the system, but the term we're looking for refers to the connecting piece from the individual vents to that main line. An AAV is an air-admitting valve, which is a different device that allows air in without venting directly to the atmosphere.