What specific design does a circuit vent serve?

The correct answer focuses on the specific design function of a circuit vent, which is intended to serve multiple plumbing fixtures connected to a single venting system. Circuit venting is a method used in plumbing that allows for the venting of several fixtures while minimizing the number of vents required.

Circuit vents are typically used in systems where fixtures are located close together, often within the same bathroom or kitchen area. This type of venting provides ventilation for multiple fixtures, allowing for the free flow of air and gases, and preventing the siphoning of traps when water flows through the pipes. It serves a dual purpose: it alleviates pressure changes within the drainage system and ensures that the traps remain filled with water to block sewer gases effectively.

This is distinct from other options. Individual fixture venting refers to venting that is dedicated to a single fixture, while combined sewer and venting would suggest a different system design, not focused specifically on circuit venting. General plumbing systems encompass a broader range of plumbing designs and do not specifically address the unique function that a circuit vent serves.