Abstract: The present invention relates to a filter unit, and a filtering system using the filter unit, comprising a housing having a longitudinal axis and an inlet and outlet for fluid containing solid contaminants and a back-flush inlet and back-flush outlet for cleansing fluid. This housing contains a substantially cylindrical filter element which has a longitudinal axis coincident with the longitudinal axis of the housing. The filter element has disposed within it a conduit, adapted to be opened to atmospheric discharge, having a longitudinal axis coincident with the longitudinal axis of the filter element. The conduit also has disposed along its surface cleansing members, which extend from the conduit to the filter element and have apertures to allow the cleansing fluid to flow through the members and into the conduit.