fluid flow of liquid and suspended solids as they sequentially traverse the several digestion tanks or stages it should be evident from the above specification that the objectives enumerated above and others are accomplished by the self contained closed system aerobic sewage treatment system of this invention sewage deposited in the bowl drops into the main digestion tank where it is vigorously agitated and broken down in the first chamber just below the bowl opening with this invention the larger solids are now preferably retained in the chamber where the greatest degree of aerated rolling action is occurring the liquid portion of the waste and smaller solids drift into the second chamber over the weir then the unique configuration of the quiescent zone of the main digestion tank performs a good separation of the small solids and liquid from the larger solids the latter are recirculated for further digestion the smaller solids and the liquid then pass on to the successive digestion tanks for further aeration until pure water is obtained in these secondary tanks the continued rolling motion the shape of the tank the use of an aeration deflector and the shape of the quiescent zone all contribute to attainment of pure water in the last stage now a truly self contained closed system aerobic sewage treatment system has been accomplished the present disclosure includes that contained in the appended claims as well as that of.