A flush tank water closet shall be equipped with an anti-siphon back-flow preventer located a minimum of how many inches above the opening of the overflow pipe?

The proper placement of an anti-siphon back-flow preventer is crucial for maintaining the integrity of the water supply and preventing contamination. In the case of a flush tank water closet, the standard requirement is that this device must be located a minimum of 1 inch above the opening of the overflow pipe.

This 1-inch clearance is important because it ensures that any potential backflow of contaminated water from the toilet bowl or tank does not reach the clean water supply. By placing the anti-siphon device at this specified height, it effectively prevents siphoning action from occurring, which could otherwise draw dirty water back into the potable water system. This practice is essential for safeguarding public health and maintaining clean drinking water standards.

When considering the options provided, 1 inch complies with plumbing codes which are established to protect against cross-connections. Higher clearances such as 2, 3, or 4 inches, while they may offer additional safety, are not the minimum requirement for this installation. Thus, the correct answer reflects both regulatory standards and practical application in plumbing design.