What type of system of waste piping uses horizontal wet venting for sinks or floor drains?

The correct answer emphasizes the combination waste and vent system as it integrates both waste removal and venting into a singular piping arrangement. In this system, horizontal wet venting allows for the drainage from sinks or floor drains to share a common vent. This configuration not only simplifies the plumbing design but also maintains proper air circulation within the waste system to prevent siphoning of traps.

In this type of system, the horizontal wet vent acts as both a drain for wastewater and a vent for the air within the pipes. This setup is particularly useful in scenarios where multiple fixtures are close to one another, enabling efficient routing of waste and air without the need for additional vent pipes.

Unlike other systems such as building subdrains, cesspools, or circuit vents, which serve different functions or adhere to varied code requirements, the combination waste and vent system is specifically designed to accommodate multiple fixtures in a cohesive manner.