Plumbing vents (a network of pipes that carry air and gas outdoors through a pipe ... allowing harmful sewer gas to enter your home. A regular kitchen sink adjacent to a wall has a vent pipe ...

The vent hole allows air to enter behind the liquid ... An example would be plumbing for a freestanding sink on a kitchen ...

When that line becomes obstructed or improperly vented, wastewater can flow back into the sink instead of draining away as intend ...