In our modern day plumbing system, a plumbing vent, or drain waste vent is the part of the system that removes sewage and greywater from the building and regulates air pressure in the pipes to facilitate flow. All fixtures and appliances must contain a trap to prevent sewer gases from leaking back into the house. Through this trap, the toilet is connected to the waste line, which in turn is connected to a soil vent pipe. At the building’s lowest point, the drain waste vent is attached, and rises inside the wall to and out of the roof. The waste is removed from the building through the drain and out through the sewer line.
The venting system consists of pipes leading from waste pipes to the outdoors usually through the roof. Vents provide a means to release sewer gases outside instead of inside the house. Vents also provide a way of equalizing the pressure on both sides of the trap, thereby allowing the trap to hold water, which is needed to maintain the effectiveness of the trap.
Without the help of plumbing vents, water and waste would not move properly through the pipes of your home. Venting helps maintain neutral air pressure within the drains, and as a result, allows gravity to successfully pull the water and waste through the pipes and drains.
Your pipes exist in one of two formats. If water is not flowing through them, the pipe is able to maintain neutral air pressure compared to its surrounding atmosphere. Once waste water begins to move, however, the air downstream begins compressing. This creates positive pressure in the pipe. The air upstream pulls like a vacuum, which pulls back on the waste.
Positive pressure in the pipes must be released. Air flow comes in behind the waste stream, pushing it forward. The volume of waste determines how much pushing or suctioning occurs.
According to building codes, every appliance in your home must have a trap. In addition, every fixture must also have a vent.
These vents must be placed somewhere within a five foot radius of your appliance. Therefore you will have a vent within a five foot radius of such items as your sinks, your toilets, your bathtub and your shower.
It is common for a plumbing vent to become blocked. Ice build up can occur in the winter, or even the body of a dead animal if it gets caught looking for warmth or a home. And if its old, it can soften and begin breaking down with age.