What is a loop vent primarily used for?

A loop vent is primarily utilized to serve two or more floor outlet fixtures that are connected to a common drainage system, especially when those fixtures are too far apart to connect directly to a traditional venting system. This type of venting arrangement allows air to circulate within the drainage system, which helps maintain proper pressure and prevents siphoning from traps in the plumbing fixtures, thus effectively venting multiple fixtures without requiring a vent stack for each individual fixture.

The design of a loop vent creates a continuous pathway that enhances ventilation for the drainage pipes while ensuring adequate drainage and trap protection. The loop configuration is specifically beneficial in preventing issues related to drainage flow and trap seal loss, especially in scenarios where multiple fixtures discharge into a common waste line.

Other options do not accurately represent the primary function of a loop vent. While connecting to a water source, venting sewage directly into the sewer, or preventing backflow may be important aspects of plumbing systems, they do not capture the specific purpose of loop vents in providing ventilation for multiple fixtures.