A method of improving the quality of septic tank effluent is disclosed. Sewage wastewater having a significant concentration of waste solids is flowed to a septic tank. In the septic tank the solids are allowed to separate from the wastewater to form a relatively clear horizontal liquid layer between sludge and scum layers. At least a portion of the liquid layer is flowed from a recirculation outlet through an aerobic filter to produce a filter effluent. The filter effluent is flowed to the septic tank. A septic tank effluent is discharged from a septic tank discharge outlet which is spaced apart from the inlet and which is in fluid communication with the liquid. The septic tank effluent has reduced levels of total nitrogen, BOD and total suspended solids.