drain waste and vent

Whether your home is on a sewer or septic system, the systems within your home are essentially the same. Drainage systems do not depend on pressure, as supply systems do. Instead, waste matter leaves your house because the drainage pipes all pitch, or angle, downward towards the sewer. Gravity pulls the waste along. The sewer line continues this downward flow to a sewage treatment facility or a septic tank.

While the system sounds simple, there's more to it, including vents, traps and clean outs. The vents sticking up from the roof of your house allow air to enter the drainpipes. If there were no air supply coming from the vents, wastewater would not flow out properly and the water in the traps would need to be siphoned away.