Illinois Plumbing Code Practice

The minimum diameter requirement for portions of the drainage system installed underground or below a basement or cellar is indeed specified by the Illinois Plumbing Code to ensure proper flow and ventilation. The correct answer, which is 2 inches, is established to accommodate standard waste and drainage practices while minimizing the risks of clogs and backflow.

Options indicating smaller diameters, like 1 inch, would not provide adequate capacity for proper drainage, thereby increasing the likelihood of blockages. Larger diameters, such as 3 or 4 inches, although capable, exceed the minimum necessary specifications for typical applications, potentially leading to excessive costs and unnecessary use of materials without providing a tangible benefit in many common situations. Hence, adhering to the established minimum of 2 inches is essential for balancing efficiency and effectiveness in plumbing systems installed below ground.