How are two fixtures connected to a common vented drainage line referred to?

The term used to refer to two fixtures connected to a common vented drainage line is "a wet vent." In plumbing systems, a wet vent is a type of venting arrangement that allows a drain from one fixture to vent another fixture's drainage. This is particularly useful in situations where two fixtures are located close together, as it can reduce the number of vent pipes required and can help maintain proper drainage and air pressure within the system.

In a wet vent configuration, the waste from one fixture may flow through the vent pipe of another fixture, effectively allowing both drainage and venting to occur through the same pipe. This method relies on the principle that the flow of wastewater helps to keep the air pressure balanced within the plumbing system, minimizing the risk of siphoning and ensuring proper drainage.

For instance, a lavatory and a toilet closely positioned can share a common vent. The wet vent allows the lavatory to serve as a vent for the toilet's drain. Such configurations must adhere to specific plumbing codes to ensure they function safely and effectively. Recognizing these principles is vital for mastering plumbing concepts and designing efficient drainage systems.