What is the purpose of a vent pipe in a drainage system?

The purpose of a vent pipe in a drainage system is to provide air circulation and protect trap seals. Vent pipes are crucial for maintaining equal air pressure in the drainage system, which facilitates the smooth flow of wastewater. When water drains from fixtures, it creates a vacuum that can affect the trap seals of plumbing fixtures. These seals prevent sewer gases from entering the living spaces. By allowing fresh air to enter the drainage system through the vent pipes, they help to equalize the pressure and keep the trap seals intact, thereby enhancing the overall efficiency and safety of the plumbing system.

The other choices do not accurately describe the role of a vent pipe. While allowing light into the drainage system may seem beneficial, it is not a function of plumbing ventilation. Assisting in liquid drainage is primarily the role of the drain pipes themselves, not the vent pipes. Containing special waste is a function of specific types of systems, but not related to the general function of vent pipes.