A low-pressure pipe system serves sites where gravity alone cannot get wastewater to a suitable drainfield — because the field is uphill, far away, or spread across shallow soils. Two tanks do the work at the front of that system.
Wastewater from the building enters the septic tank first. Inside, quiescent conditions separate the flow into three layers: scum floating on top, sludge settling to the bottom, and relatively clear effluent in the middle. Anaerobic bacteria digest a portion of the solids continuously. Baffles at the inlet and outlet keep the layers undisturbed and prevent solids from carrying over.
Sizing follows the design daily flow, with enough volume to hold a multi-day retention time. Two compartments improve separation, and an effluent filter on the outlet catches the fine solids that would otherwise reach the pump tank.
Clarified effluent flows by gravity into the pump tank, a separate watertight chamber holding a submersible effluent pump, a float or transducer control set, a check valve, and a union for servicing. Floats set the pump-on and pump-off elevations, and a third float above them triggers a high-water alarm.
The tank includes dedicated storage above the working range — usually at least a day of design flow — so a power outage or a pump failure does not back the system up into the building before anyone notices.
The pump discharges measured doses through a small-diameter pressure main to the perforated laterals in the drainfield. Dosing distributes effluent evenly across the entire field and allows the soil to drain and re-aerate between cycles, which is what keeps a field working for decades.
Pump the septic tank on schedule, clean the effluent filter, test the alarm, and exercise the pump. These systems are reliable when they are serviced and expensive when they are not.