Which of the following is not considered a type of lavatory?

The correct answer pertains to the classification of lavatory types. A reverse trap is not classified as a type of lavatory. Instead, it refers to a plumbing configuration associated with waste drainage, where the trap is oriented differently to accommodate specific plumbing designs.

On the other hand, the other options represent recognized styles of lavatories. Splash-back and ledge-back refer to designs that include features for preventing water from splashing onto walls or adjacent surfaces; they are integral in bathroom designs where control of water flow is essential. Countertop models refer to lavatories that are mounted on a countertop, showcasing both functionality and aesthetic appeal in modern bathroom designs. Understanding these distinctions is essential in the realm of sanitation and installation, as they inform both the design and the practical aspects of restroom functionality.