An effluent filter comprises multiple, generally cylindrical filter elements (4) radially mounted on a hollow spindle (5), which also serves to discharge filtrate (16). The filter elements are rigidly attached to the spindle which is sealed by at least two double seal units (17, 18), which have pressurized clean fluid fed between each seal pair to prevent ingress of dirty liquid into the filtrate (16). The seal fluid may be water, lubricant fluid, or gas e.g. air. The filter element assembly has a pulley (9) attached to the spindle, and is rotatable via a belt drive from a motor (8) located above the sump liquid level. The spindle (5) may be perforated and contain a distributor lance (10) to allow a cleaning medium e.g. compressed air to be released below the uppermost filter elements and provide a degree of fouling removal from the elements.