Vents provide a means to release sewer gases outside instead of inside the house.
Waste vent roof.
Instead they serve to equalize air pressure within the dwv system and also release sewer gases into the outdoor air as all vent pipes terminate through the roof.
Through the stack sewer gases are carried up to the roof through vent lines.
A true vent is a vertical pipe attached to a drain line that travels through the roof with no water running through it.
Many fixtures are not so conveniently located however and other solutions must be found.
The venting system or plumbing vents consists of a number of pipes leading from waste pipes to the outdoors usually through the roof.
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Because sewer gases may flow back up into the building drain piping from a public sewer or private septic system and because some sewer gases are included in building waste flowing through the piping the plumbing vent system needs to carry these gases outside usually above the building roof where they are disposed of safely and without leaving unpleasant or possibly dangerous smells and gases inside the building.
Drain pipes take the wastewater to the soil stack.
Water and waste head down the pipe while gasses are vented up and outwards.
If a fixture is close to the stack and on the top floor the upper part of the stack serves nicely as a vent.
The stack pipe leads the whole way out through your roof and further underground in the opposite direction to main sewer lines.
Behind the wall where you can t see a vent line and drainpipe lead to a soil stack which is the control center of the wastewater system.