Final answer:
The fixture that functions as a dry vent connection to a horizontal wet vent is called a vent stack (option 1). It allows air into the plumbing system and prevents the formation of a vacuum, ensuring proper drainage.
Step-by-step explanation:
The fixture that serves as a dry vent connection to the horizontal wet vent is known as a vent stack. This is essential for various types of plumbing systems and it serves to provide air to the system, ensuring that water and waste move properly through the drain pipes by preventing a vacuum from forming in the system.
A vent stack is typically connected to the building's main drain-waste-vent system and extends through the roof, allowing sewer gases to be safely released outside the building. Unlike wet vents, which can carry both air and water, dry vents only carry air. In some cases, a dry vent may also be referred to as a vent pipe or stack vent.