Which of the following is NOT a type of plumbing fixture?

A manhole is not classified as a plumbing fixture because it is primarily part of the sewer system rather than a fixture used for water distribution or sanitation within a building. Plumbing fixtures are defined as devices that receive water and are designed to perform a specific function, such as delivering or draining water. Toilets, sinks, and bathtubs all serve as essential components for using and managing water in residential and commercial spaces, making them integral to plumbing systems. A manhole, however, serves as an access point for maintenance and inspection of underground utility systems and is not used directly by occupants for sanitation or water usage. This distinction is crucial in understanding the roles and definitions of various components within plumbing systems.