In plumbing, at what distance should venting for a drain generally occur?

In plumbing, venting for a drain is typically required to be installed when the horizontal distance from the fixture to the vent exceeds 20 feet. This is important because proper venting ensures that air can enter the drainage system, which prevents the formation of a vacuum that could impede the flow of wastewater and potentially lead to problematic plumbing issues such as siphoning traps.

By establishing a venting system at this distance, it helps maintain the pressure equilibrium within the pipes, allows for the efficient removal of waste, and reduces the risk of foul odors entering living spaces. The code specifies this distance to ensure optimal functionality of the plumbing system and compliance with safety and sanitary standards.