Molded septic tank

A septic tank is formed from a plurality of tank modules each of which comprises a substantially closed container. Each tank module is bolted to a next adjacent tank module at a flat end wall thereof with the bolts being of large diameter and in some cases including a central longitudinally extending opening so that the bolts act to communicate fluid from one tank module to the next adjacent tank module. Each tank module is shaped with an upper wall part which is of parabolic arch shape and a base wall which is substantially flat. This defines the optimum shape for strength to accommodate the forces when the tank is buried. Tanks can thus be formed in modular parts so that various different size modules can be connected together by the above coupling technique to form a multitude of different sizes of tank. An access opening in the upper wall is defined at the junction between two tank modules with the central dividing walls between the tank modules being cut down to allow a person to enter either of the tank modules from the single access opening. The tank provides a required strength at minimum wall thickness and also the end walls automatically provides bulkheads for dividing one septic compartment from the next.