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Claim 1

A FILTER BOTTOM FOR A LIQUID FILTER, SAID FILTER BOTTOM COMPRISING A PLURALITY OF FILTER BLOCKS ARRANGED IN PARALLEL ADJACENT ROWS, SAID ROWS OF BLOCKS EXTENDING SUBSTANTIALLY THROUGHOUT THE ENTIRE FILTER AND SUPPORTING A BED OF FINELY DIVIDED FILTERING MEDIUM ADAPTED TO FILTER A LIQUID DURING DOWNFLOW THROUGH THE BED AND TO PERMIT THE REMOVAL OF CONTAMINANTE MATERIAL DURING UPFLOW OF A WASH MEDIUM, EACH BLOCK HAVING UPPER AND LOWER HORIZONTAL FLOW PASSAGES THERETHROUGH, THE UPPER AND LOWER HORIZONTAL FLOW PASSAGES THERETHROUGH, THE UPPER FLOW PASSAGES OF THE BLOCKS IN EACH ROW BEING IN END-TOEND COMMUNICATION WITH ONE ANOTHER TO PROVIDE A SERIES OF INDIVIDUAL, PARALLEL AND CONTINUOUS UPPER FLOW CONDUITS EACH OF WHICH EXTENDS FROM ONE SIDE OF THE FILTER BOTTOM TO THE OPPOSITE SIDE, SAID UPPER FLOW CONDUITS PROVIDING FOR LIQUID FLOW HORIZONTALLY ALNG THE LENGTH OF EACH UPPER FLOW CONDUIT BUT SUBSTANTIALLY PREVENTING TRANSVERSE HORIZONTAL FLOW BETWEEN UPPER FLOW CONDUITS, THE LOWER FLOW PASSAGES BEING SIMILARLY ARRANGED IN ENDTO-END COMMUNICATION WITH ONE ANOTHER TO PROVIDE LOWER FLOW CONDUITS WHOSE LONGITUDINAL AXES ARE ORIENTED LOWER FLOW CONDUITS WHOSE LONGITUDINAL AXES ARE ORIENTED PARALLEL TO THE LONGITUDINAL AXES OF THE UPPER FLOW CONDUITS, A PLURALITY OF PORTS INTERCONNECTING EACH LOWER FLOW CONDUIT WITH AN UPPER FLOW CONDUIT, SAID PORTS BEING EQUALLY SPACED IN A STRAIGHT LINE PARALLEL TO THE CONDUIT LENGTH, THE RATIO OF THE PORT DIMENSION TAKEN IN THE DIRECTION OF FLOW ALONG THE LOWER FLOW CONDUIT T THE HEIGHT OF THE LOWER FLOW CONDUIT BEING NOT MORE THAN ABOUT 0.20, PASSAGE MEANS THROUGH THE TOPS OF THE BLOCKS IN THE COMMUNICATION WITH THE UPPER FLOW CONDUITS, A FLUME EXTENDING THE FULL DISTANCE BETWEEN OPPOSITE SIDES OF THE FILTER, SAID FLUME BEING ORIENTED TRANSVERSE THE LOWER FLOW CONDUITS, A PARTITION BETWEEN THE INTERIOR OF THE FLUME AND THE INTERIOR OF THE LOWER FLOW CONDUITS, EACH OF THE LOWER FLOW CONDUITS BEING IN COMMUNICATION WITH THE FLUME THROUGH APERTURE MEANS IN SAID PARTITION, THE SIDE WALLS OF THE LOWER FLOW CONDUITS OF THE ROW OF BLOCKS IMMEDIATELY ADJACENT SAID FLUME BEING CUT AWAY TO PROVIDE A FLOW MANIFOLD INTERCONNECTING THE LOWER FLOW CONDUITS, AND MEANS FOR FEEDING WASH MEDIUM INTO THE FLUME AND EFFECTING FLOW THEREOF THROUGH THE MANIFOLD AND LOWER FLOW CONDUITS AND UPWARDLY THROUGH THE UPPER FLOW CONDUITS AND THE FILTER BED.