What is the common purpose of venting in a plumbing system?

Venting in a plumbing system primarily serves to equalize pressure within the drainage system. When water flows through pipes, it can create negative pressure, which may impede the flow or cause drains to siphon and lose water in traps, leading to potential sewer gas entry into buildings. Vent pipes allow air to enter the system, which prevents these pressure fluctuations and ensures that waste and wastewater can flow freely through the drainage pipes. Additionally, proper venting helps in maintaining the water seal in traps that prevent sewer gases from entering living spaces.

The other options do not correctly capture the primary purpose of venting. Venting does not transport waste; that is the role of the drainage pipes. It also does not prevent flooding in stormwater systems, as that involves separate drainage systems designed for surface runoff. Finally, venting is not involved in heating water for fixtures, which is a function of water heating systems. Thus, equalizing pressure is the central purpose of venting in plumbing.