On a 4-inch mop sink waste that is extended 38 feet from its connection on a horizontal main, what is the minimum size vent required?

In plumbing design, venting is crucial for maintaining proper drainage and preventing the siphoning of traps. For a 4-inch mop sink waste that is extended 38 feet from its connection on a horizontal main, it's important to ensure that adequate ventilation is provided for the drainage system.

According to plumbing codes, a vent pipe must be sized appropriately based on the size of the drain it services and the distance it runs. Generally, for a 4-inch waste line, when determining the minimum size of the venting requirement, the guidelines suggest that the vent should be at least half the diameter of the drain line. Therefore, a 4-inch drain would typically require a vent of at least 2 inches to effectively manage the air pressure change within the drainage system.

This minimum vent size helps to ensure efficient drainage without risking a blockage, as it allows for the proper escape of air and prevents the creation of negative pressure that could lead to trap siphoning. Thus, the minimum size vent required for a 4-inch mop sink waste extending 38 feet from the main connection is indeed 2 inches.