Abstract: Effluent flows into a settling pipe channel or conduit and is prevented from discharge while the solids are settling, by means of airlocks. When the solids have settled, one airlock is opened and the clarified effluent is drawn off and replaced by unclarified effluent at which time the one airlock is closed. When the pipe or the like requires cleaning of solids, the other airlock is opened and untreated effluent is used to scour out the pipe or channel and return the solids to the main settling pond to assist in aerobic action. A plurality of pipes or the like can be automatically sequenced so that continuous clarification and purging is carried out.