Abstract: A filtering arrangement is provided for effluent from a septic tank prior to passage to a drain field or other disposal. The filtering arrangement makes use of an open-top, U-shaped filter means into which the septic effluent is conducted from the top, preferably through a T-fitting providing an open-topped channel leading into the U-shaped filter. The filter may be formed of an outer perforated casing and an inner lining of an open-cell-type polymeric material which effects the filtering of the effluent. The U-shaped filter is preferably suspended from the T-fitting. A preferred filter includes an inner and outer casing with a fibrous filter material between. The filter also preferably has an imperforate lower portion to retain a permanent body of liquid in the bottom of the filter. The arrangement provides fail-safe filtering automatically adjustable for varying flow rates and conditions of the filter. The polymeric filter medium is changed periodically to maintain efficiency.