A residential automatic washing machine shall have a _______ stand pipe extended to at least ______ above the flood level rim of the washing machine.

The requirement for a residential automatic washing machine to have a standpipe that is 2 inches in diameter and extended to at least 18 inches above the flood-level rim of the washing machine is important for several reasons.

First, the 2-inch diameter of the standpipe allows for sufficient drainage capacity to handle the flow of water from the washing machine, which can discharge large volumes quickly, particularly during the spin cycle. Using a diameter larger than 1 inch ensures that the pipe can handle the volume without causing significant back pressure or overflow.

Second, extending the standpipe to at least 18 inches above the flood-level rim prevents the risk of water backing up into the washing machine. The flood-level rim is essentially the point above which water could overflow from the machine. By ensuring that the standpipe is elevated to this specific height, it reduces the potential for siphoning or overflow, which could lead to water damage or create unsanitary conditions.

The other options do not meet the necessary criteria for either diameter or height, thereby creating risks in residential plumbing systems associated with drainage and overflow issues. Ensuring proper installation according to these specified dimensions promotes the overall safety and effectiveness of the plumbing system in residential environments.