What is the minimum pipe size for a maximum size of any combination waste and vent drainage line?

• A. 2 Inches
• B. 4 Inches
• C. 6 Inches
• D. 3 Inches

Answer: (B)

A combination waste and vent line is a single pipe that handles both wastewater and venting for a system, and codes cap how large this line can be to ensure proper venting and drainage behavior. The largest size allowed for a CWV line is four inches in diameter. Therefore, the smallest pipe that can still serve as the maximum-sized CWV line is four inches. A smaller diameter like two or three inches wouldn’t reach the maximum allowed size, while a larger diameter such as six inches would exceed the permitted limit.