In what scenario might a combination waste and vent system be used?

A combination waste and vent system is utilized primarily in scenarios where individual venting for each fixture becomes impractical or challenging. This type of system allows for both waste removal and venting functions to be handled by the same piping, which simplifies the plumbing layout.

In situations where space is limited, such as in dense urban buildings with multiple plumbing stacks, it may not be feasible to run separate vent pipes for every single fixture. The combination system effectively reduces the number of pipes needed and helps maintain proper venting for the drainage flow, which is crucial for preventing siphoning of traps and ensuring that gases can escape the drainage system safely.

The other provided choices, such as maximizing water flow to the main drain, reducing the number of fixtures, or enhancing cost efficiency in larger buildings, do not directly address the primary purpose of a combination waste and vent system, which centers around the practicality of venting solutions within restricted or complex spaces.