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.
Waste vent roof.
The stack pipe leads the whole way out through your roof and further underground in the opposite direction to main sewer lines.
Water and waste head down the pipe while gasses are vented up and outwards.
The venting system or plumbing vents consists of a number of pipes leading from waste pipes to the outdoors usually through the roof.
The vent pipes are part of the drain waste vent or dwv system of a house or building and they do not carry water inside them.
Drain pipes take the wastewater to the soil stack.
Vents provide a means to release sewer gases outside instead of inside the house.
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.
Many fixtures are not so conveniently located however and other solutions must be found.
The stack also allows fresh air in to keep water running smoothly through your piping.
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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.