Which of the following would NOT be classified as a part of a vent system?

A drainage pipe is primarily designed to carry wastewater away from fixtures and is not considered a component of a vent system. The purpose of a vent system is to allow air to enter the plumbing system to maintain atmospheric pressure and facilitate proper drainage. This prevents the creation of a vacuum that can hinder the flow of wastewater, as well as helps to release sewer gases outside the building.

The other options listed—vacuum breaker, trap seals, and vent pipe—are all integral to a vent system. A vacuum breaker helps prevent back siphonage, trap seals are necessary to maintain a water barrier that prevents harmful gases from entering indoor spaces, and vent pipes are essential components in providing air circulation within the plumbing system. Thus, the clarification that a drainage pipe does not fit into the classification of a vent system is what makes this answer appropriate.