Abstract: A septic tank for use with a leaching pool is provided which has a cylindrical portion forming a chamber for treatment of raw sewage. A ring encircles the cylindrical portion for mounting the septic tank on the upper wall edge of the leaching pool. Positioning haunches or centering elements are also provided which automatically center the septic tank on the leaching pool. An inlet baffle and an outlet baffle are also provided in the septic tank with each having an open top for alignment with a viewing opening formed in a cover provided for the septic tank. The outlet baffle leads into a passageway formed by a reinforcing member extending downwardly from the upper portion of the cylindrical portion. The cylindrical member, the ring, the positioning haunches, and the reinforcing member are all monolithically formed of precast concrete.