What defines a continuous vent in plumbing?

A continuous vent in plumbing refers specifically to a vertical vent that continues the path of the vertical drain. This type of vent allows for the free flow of air and helps maintain proper pressure within the drainage system, which is essential for preventing siphoning and ensuring that waste can flow freely without obstruction.

The function of a continuous vent is to challenge gravity and allow gases and air to escape from the drainage system. When it rises vertically as part of the drainage stack, it provides venting directly above the highest fixture, connecting to the main vent stack as needed for effective air circulation and drainage operations. This ensures that wastewater can flow efficiently and that the risk of trap siphonage is minimized.

In contrast, the other options describe different types of vents that do not meet the specific criteria for a continuous vent. For example, a vertical vent that begins at the highest fixture defines a venting method that may not necessarily connect to the drainage stack directly; and a horizontal vent is not considered a continuous vent because it does not maintain a vertical orientation throughout its length. A vent designed for cross-connection control also serves a different purpose and does not establish a continuous relief path for drainage.