Vent pipes are important.

Vent pipes are important.

Vent pipes connect to your drains and they run directly to your roof or horizontally to another vent pipe that goes to your roof. Without them wastewater flowing down your drain would cause your s-traps to empty due to a siphoning action and then sewer gases could enter your house. The vent pipe allows outside air to enter and break the siphon action caused by the wastewater flow.