The plumbing vent goes beyond the roof of a property and allows sewer gases and air to make their way out of the wastewater system. It also allows for the equalising of air pressure in the plumbing system as water makes its way in once flushing toilets, sinks, or tubs are drained. Provided that it was set up correctly in the home, the vent can help provide for a very smooth flow of wastewater. It also prevents sewer gases from making their way into the living spaces.

Pipe Size
The diameter of the wastewater pipe is the only factor that determines the most distance a vent may be located from a fixture. If a wastewater pipe connected to a fixture measures only 1 ¼ inch, the vent pipe should be located within thirty inches of the fixture. A pipe with that size supports only one fixture, preferably a tub or sink. If, however, the wastewater pipes connected to a fixture measure four inches, the vent can be placed ten feet away from the plumbing fixture. Wastewater pipes with that size are capable of supporting more than a hundred plumbing fixtures.

Measure From the Trap
Horizontal distance should be measured from vent pipe to the part of the p-trap closest to it. Usually, the trap sits right under a sink or a drain and might be farther from the vent than the end of the fixture.

Recommended Vent Pipe Measurements
Attach a 1 ¼ inch vent pipe to a 1 ¼ inch wastewater pipe. Larger wastewater pipes can be vented with smaller pipes. For example: you can use a three-inch vent pipe to vent a four-inch wastewater pipe. Vent pipes should extend six to twelve inches above the roof.

Vent Maintenance Tips
On occasion, drain vents can become clogged with debris, causing water to drain slowly and annoying gurgling sounds to develop. Vents usually get clogged due to ice building up in it during the winter season. This happens when air that rises up the vent freezes in the vent pipe and becomes ice crystals.

Plumbing vents also get clogged due to leaves falling deep in them.

Regardless of the reason why the vent got clogged, clearing it requires that you contact a plumber. He will scale the roof and squirt water down the vent opening for you. Although you can do this task yourself, reputed plumbers assure you of quality work, since they have the best tools and safety equipment for the job.