The fixture drain of an automatic clothes washer shall connect to a minimum ____ -inch branch drain.

The requirement for the fixture drain of an automatic clothes washer to connect to a minimum 3-inch branch drain is based on the potential volume of wastewater generated by the appliance. Clothes washers typically discharge a significant amount of water, and ensuring that the drain line is adequately sized is crucial for preventing clogs and ensuring proper drainage.

A 3-inch drain allows for the passage of larger volumes of water and can accommodate the discharge more effectively than a smaller diameter pipe. Additionally, by using a larger branch drain, the plumbing system can better handle sudden surges of water that occur during the washing cycle, which can include both the initial fill and the high-volume discharge of wastewater. This sizing helps maintain a smooth flow and reduces the likelihood of backup or flooding.

Choosing a smaller diameter than 3 inches, such as 1 1/2 inches, 2 inches, or 2 1/2 inches, may be inadequate for the demands of a washing machine, leading to potential plumbing issues that can result from improper drainage, such as slow drains or overflow. Therefore, plumbing codes specify the 3-inch connection to ensure reliable and effective drainage for automatic clothes washers.