What is the trap size for a water closet that uses more than 1.6 GPF?

The trap size for a water closet, particularly those that use more than 1.6 gallons per flush (GPF), is typically required to be 3 inches in diameter. This is significant because toilets with higher flush volumes demand a larger trap to accommodate the increased flow of wastewater, ensuring efficient drainage and reducing the risk of clogs.

Using a 3-inch trap enhances the hydraulic performance of the plumbing system, allowing for the rapid removal of waste and preventing backflow or drainage issues that may arise with smaller trap sizes. In plumbing codes, the minimum size for a trap for water closets using more than 1.6 GPF is often specified specifically as 3 inches, in order to meet the demands of modern fixtures and maintain a functional waste removal system.

Smaller trap sizes may be adequate for toilets that use less than 1.6 GPF, but with higher flow rates, it's crucial to have the larger 3-inch trap to ensure optimal performance.