What is a vent stack used for in plumbing?

The primary purpose of a vent stack in plumbing is to ventilate the plumbing system and equalize pressure. This function is crucial because it allows air to enter the plumbing system, which helps prevent vacuum conditions that can impede drainage flow. When wastewater is discharged from fixtures into the drainage system, it can create negative pressure. A properly functioning vent stack allows air to replace the volume of the wastewater and maintain balance in the system, ensuring that drainage occurs smoothly.

Additionally, the vent stack helps to prevent sewer gases from entering the home by allowing these gases to escape safely above the roof level. This is essential for maintaining indoor air quality and ensuring that the plumbing system is operating effectively.

The other options describe functions that do not align with the specific role of a vent stack. Connecting multiple drainage pipes pertains more to drain systems, supplying fresh air to water tanks relates to air supply, and draining excess water describes a drainage function rather than venting. Thus, the function of ventilating and pressure equalization distinctly defines the importance of the vent stack in plumbing systems.