Illinois Plumbing Code Practice Exam 2025 – All-in-One Guide for Exam Success!

The minimum drain size required for all laundry/washer boxes is 2 inches. This is based on the plumbing code's requirements to ensure proper drainage capacity for the high flow rates associated with washing machines. A larger drain size is critical because washing machines can discharge a significant volume of water quickly, especially during the spin cycle.

Using a 2-inch drain minimizes the risk of clogs and backs-ups, allowing for better movement of water and waste away from the laundry area. Smaller drain sizes, such as 1 inch or 1.5 inches, would not be sufficient to handle the volume effectively, while a 2.5-inch drain is larger than necessary for standard washing machine discharges, making 2 inches the ideal minimum size.