Final answer:
The parallel vent stack should be connected to the drainage stack using a Y-fitting or combination Wye and eighth-bend to ensure smooth flow and prevent blockages.
Step-by-step explanation:
The parallel vent stack shall be connected to the drainage stack by means of a Y-fitting or combination Wye and eighth-bend (not just a single elbow). This type of fitting is used because it allows for a smoother flow of waste and vent air. Connecting a parallel vent stack typically requires fitting configurations that provide directional change while minimizing the potential for blockages and maintaining a steady flow in the drainage system. Fittings like tees or elbows are generally not suitable for this application as they can lead to obstructions or interference with the flow within the parallel systems.