What do you call the drain from the trap of a fixture to where it connects with any other drain pipe?

The term used to describe the drain from the trap of a fixture to where it connects with any other drain pipe is "Fixture Drain." This is a standard designation in plumbing terminology, indicating a specific section of the drainage system that serves a particular fixture, such as a sink, toilet, or bathtub. The function of the fixture drain is to provide a pathway for wastewater to exit from the fixture's trap and continue through the drainage system.

While the other options may sound plausible, they do not accurately reflect the widely accepted terminology used in plumbing codes. "Exit Drain," for example, is not commonly recognized in industry standards, and "Trap Drain" suggests that the focus is exclusively on the trap rather than the entire drainage pathway from the trap to the larger system. "Drain Connection," while it implies a point of connection, does not specifically denote the part that lies immediately after the trap leading to the building's drainage system. Therefore, the accurate and accepted term for this part of the drainage system is indeed the Fixture Drain.