A plumber is installing a main soil or waste stack in a multi-story building. What is the primary purpose of connecting a stack vent, originating from the top-most soil or waste stack, to the open air?

Question: A plumber is installing a main soil or waste stack in a multi-story building. What is the primary purpose of connecting a stack vent, originating from the top-most soil or waste stack, to the open air?

Answer options:

• To provide a direct path for the removal of sewage from the building. ✅ To prevent backpressure and allow atmospheric pressure equalization in the drainage system.
• To introduce fresh air into the drainage system for odour control.
• To facilitate the inspection and cleaning of the drainage pipes.

Correct answer: To prevent backpressure and allow atmospheric pressure equalization in the drainage system.

Explanation: The primary purpose of a stack vent is to allow for the equalization of atmospheric pressure throughout the drainage system, preventing siphonage of fixture traps and backpressure. While some air exchange occurs, the main function is pressure regulation, not direct sewage removal or odour control by fresh air. Inspection and cleaning are typically done via cleanouts.