What does a common vent specifically do?

A common vent serves as a critical component in plumbing systems, designed to provide ventilation for multiple fixtures simultaneously. This is vital for maintaining the proper pressure balance within the drainage system and allowing sewer gases to escape safely into the atmosphere. By connecting to multiple fixtures, a common vent prevents negative pressure that could cause siphoning of trap seals and subsequent sewer gas ingress into living spaces. It effectively reduces the number of vent pipes required in a plumbing system, streamlining installation and improving functionality by ensuring that all connected fixtures operate efficiently without risk of venting issues.

The other options describe functions that are not applicable to a common vent. While some may refer to a vent that serves only one fixture, that would be a dedicated vent, which operates differently. Similarly, a common vent does not gather stormwater or retain organic matter, as those are unrelated to its primary function of venting drainage systems.