If a vent pipe connects to a horizontal soil or waste pipe, the vent pipe shall rise vertically at a 45-degree angle to a point ______ inches above the fixture it is venting.

The requirement for a vent pipe to rise vertically at a 45-degree angle to a height of 6 inches above the fixture it is venting is established to ensure proper drainage and venting function within the plumbing system. This height is crucial because it helps prevent siphoning of water from traps and allows for the equalization of pressure in the waste system, thereby reducing the risk of sewer gases entering the living spaces and maintaining the overall health of the plumbing system.

Raising the vent pipe at this specific angle and height helps ensure that it is adequately positioned to allow air to enter the drainage system, promoting efficient flow and minimizing potential blockages. The height also provides sufficient clearance to connect to the vent stack, further preventing backflow and ensuring that the vent functions properly.

The incorrect options do not meet the prescribed standards set forth in plumbing codes which dictate these measurements and angles for vent pipes to ensure they perform effectively in conjunction with the overall plumbing system.