What is the minimum distance required for an air gap in a drainage system?

In plumbing systems, an air gap is a crucial feature designed to prevent backflow, which can contaminate clean water by allowing dirty or contaminated water to flow back into the potable water supply. The minimum distance required for an air gap must create sufficient separation between the water supply and potential contaminants.

The correct choice refers to "twice the diameter of the indirect waste pipe." This specification ensures that there is enough vertical separation to prevent siphoning or backflow from occurring. The larger distance effectively reduces the risk of any connection point between the clean and dirty water systems, thereby maintaining the integrity of the potable water supply.

Other options may not provide adequate separation or are not in accordance with accepted plumbing codes that prioritize safety and public health. For example, just having an air gap equal to the diameter of the waste pipe might not sufficiently prevent backflow, particularly in systems where pressure changes could create a risk. Similarly, a distance of five feet from the flood level rim may be excessive or irrelevant in certain configurations, while stating it simply as equal to the height of the drainage pipe does not provide the necessary specificity needed to ensure a proper air gap exists.

The requirement for "twice the diameter of the indirect waste pipe" ensures both compliance with plumbing standards