In what situation would you use a double sanitary tee?

A double sanitary tee is specifically designed to connect two vertical fixtures to a horizontal drainage line while maintaining the proper flow and ensuring that there's no risk of sewer gases escaping. This fitting allows for the connection of horizontal and vertical pipes, facilitating the drainage from two fixtures that run vertically down to a common horizontal drain.

This design helps in maintaining a smooth flow of wastewater, reducing the risk of blockages and promoting efficient drainage. Additionally, by allowing for these connections, a double sanitary tee provides necessary access for maintenance and cleaning.

In contrast, the other scenarios would not be best served by a double sanitary tee due to either structural or flow concerns. For instance, using it to connect drains in a vertical run could lead to improper water flow, and diverting waste to multiple directions might complicate drainage and lead to issues with backflow or inadequate venting. Connecting a vent stack requires different fittings that are designed specifically to maintain air flow and pressure balance within the plumbing system.