Abstract: A concrete block assembly for use in a septic tank sewage disposal system including a plurality of porous blocks each having multiple apertures therethrough oriented in end-to-end, sealed relationship and retained in this relationship by tension rods extending through the assembly to form a module which can be assembled at a factory site, transported to the site of installation and lowered into a trench or ditch to form part of the drain field of a septic tank disposal system. Connecting assemblies are provided for assembling a plurality of block modules in end-to-end communicating relationship to provide adequate capacity for each installation.