Abstract: Five relatively spaced apart, internal partitions separate the subject septic tank into four consecutive settling chambers, a filtration chamber and an outlet chamber. Each of the four partitions separating the settling and filtration chambers is provided with a conduit having a connective section mounted in an upper portion of the partition at least two-thirds of the distance from the bottom to the top of the septic tank and with a leg section extending downwardly from the connective section. Each leg section has a lower opening communicating with a lower portion of one of the chambers at least two-thirds of the distance from the top to the bottom to the septic tank.