How does a venting system contribute to preventing siphoning in plumbing?

A venting system plays a crucial role in the functionality of plumbing by maintaining an equal pressure within the drainage system. When water flows through the pipes during drainage, it can create a vacuum effect that may draw water out of traps in fixtures, leading to siphoning. By allowing air to enter the drainage pipes, the venting system prevents this vacuum formation, thus equalizing the pressure within the pipes.

This equalization is vital because it ensures that the water seal in traps remains intact, which keeps sewer gases from escaping into living spaces and helps maintain proper drainage flow. Without sufficient venting, the pressure differential created by draining water could lead to unwanted siphoning, adversely affecting the system's performance.

The other options, while they may be functions of the plumbing system, do not directly relate to preventing siphoning in the context of how venting operates. Therefore, the correct answer highlights the essential function of venting in maintaining pressure equilibrium within the drainage system, effectively preventing siphoning.