Illinois Plumbing Code Practice

The correct answer is that each trap shall have a water seal of 2 inches. This requirement is specified in plumbing codes to ensure that traps effectively prevent the passage of sewer gases into buildings while allowing wastewater to flow freely. A 2-inch water seal provides a sufficient barrier against odors while also accommodating drainage for typical residential and commercial plumbing fixtures.

Having a proper water seal is essential for maintaining sanitary conditions and ensuring the efficient operation of the plumbing system. While other measurements may serve a purpose in specific contexts or types of fixtures, the 2-inch requirement is standard for most traps in typical plumbing applications.