The VTR is connected to which plumbing system?

The correct choice indicates that the VTR, or Vent Through Roof, is connected to the sanitary sewer system. The purpose of a VTR is to provide ventilation for the plumbing system, specifically to facilitate the proper function of the sanitary drainage system.

In a sanitary sewer system, wastewater and sewage are transported away from various fixtures in a building. This system relies on gravity to ensure the efficient flow of waste. A VTR helps equalize pressure within the drain lines and allows sewer gases to vent outside, preventing back pressure which can lead to blockages and poor drainage performance.

In contrast, the freshwater supply system is primarily concerned with delivering clean water to fixtures, the storm drainage system deals with surface water runoff, and the gray water system collects slightly used water from baths, sinks, and washing machines for reuse, but none of these require the specific ventilation that a VTR provides in relation to the sanitary sewer. Therefore, the association of a VTR with the sanitary sewer system underscores its critical role in maintaining the safety and efficiency of the waste management process in a building's plumbing infrastructure.