If a standpipe is used for an automatic clothes washer, what should be the minimum diameter of the standpipe and its trap?

The correct minimum diameter for a standpipe used in conjunction with an automatic clothes washer is 2 inches. This requirement is based on plumbing codes and standards that aim to ensure proper drainage and ventilation in waste systems. A 2-inch diameter allows for sufficient flow capacity to accommodate the discharge from washing machines, which can generate a significant volume of water in a short period.

Using a standpipe with a diameter smaller than 2 inches can lead to issues such as slow drainage, increased risk of clogs, and potential backflow of wastewater. The trap connected to the standpipe also needs to be of the same minimum diameter to maintain consistent flow and prevent any restrictions that could disrupt the drainage system's efficiency. Having the appropriate diameter is essential for the effective functioning of the plumbing system, ensuring that it can handle the washing machine's discharge without causing water-related problems in the home.

A diameter of 1 inch would be inadequate for the water flow demands of a washing machine, while larger diameters, such as 3 or 4 inches, exceed the requirement and may not fit the plumbing design intended for residential laundry setups.