The Aerobic Treatment Plant with Filter Pipe ("ATPFP") processes sewage for buildings not connected to a municipal sewer system. It employs a multi-stage process for cleaning sewage in a single, light-weight, easy-to-install unit. Sewage is initially cleaned in the aerobic tank, which is divided into an inner chamber and an outer chamber by a funnel-shaped clarifier hanging down in the aerobic tank, with the opening in the bottom of the clarifier held above the bottom of the aerobic tank. Air droplines hang down in the outer chamber of the aerobic tank, so that sewage in the outer chamber is aerated, stimulating aerobic microorganisms which digest the sewage. The sewage in the outer chamber then moves into the inner chamber inside the clarifier where gravity separates solids from the effluent. This cleaned effluent is then drained to the post-treatment tank for additional cleaning, where it may be chlorinated before it is filtered to screen out debris and then stored for discharge. The ATPFP utilizes a filter pipe to further clean effluent and to trap debris, and the design of the filter pipe allows for easy removal for cleaning, while maximizing the time between cleanings. Typically, the ATPFP employs a pump to discharge the cleaned effluent. The ATPFP uses a single cover to seal both tanks, adding structural support while simplifying manufacture. To reduce the weight, aiding in installation, while retaining the strength and durability needed for a sewage system, the ATPFP is generally made of fibreglass reinforced plastic, and the post-treatment tank is joined to the aerobic tank by a lamination process.