A filter system especially useful in the treatment of waste material, in particular liquid waste material which may include particulate matter therein. The filter system includes a series of filters of progressively finer porosity in order to selectively eliminate particulate (or semi-particulate) matters from a carrier material, typically but not exclusively, of a fluid or liquid nature. The filters are mounted within a housing which includes an outlet port and a plurality of inlet ports, wherein each inlet port includes a check valve.