Pre-cast sectional concrete septic tank

Claim 1

A PRE-CAST CONCRETE SECTIONAL SEPTIC TANK COMPRISING, IN COMBINATION: (A) A FLAT, RECTANGULAR, PRE-CAST CONCRETE BASE SLAB CONSTRUCTION HAVING GROOVES IN ITS UPPER SURFACE, EXTENDING ALONG THE FOUR PERIPHERAL EDGES; (B) TWO OPPOSITE PRE-CAST CONCRETE END WALLS SET IN THOSE GROOVES OF THE BASE CONSTRUCTION WHICH ARE LOCATED AT THE END PERIPHERAL EDGES THEREOF, (C) OPPOSITE, PARALLEL PRE-CAST CONCRETE SIDE WALLS SET IN SAID GROOVES OF THE BASE CONSTRUCTION WHICH ARE LOCATED AT THE SIDE PERIPHERAL EDGES THEREOF, EACH OF SAID SIDE WALLS COMPRISING: (1) TWO SETS OF PRE-CAST ELONGATE CONCRETE WALL PLANKS OF THE TYPE HAVING A GREATER WIDTH THAN THICKNESS AND HAVING PARALLEL SIDE FACES, THE PLANKS OF THE SETS BEING DISPOSED END-TO-END AND IN EACH SET THE PLANKS HAVING EQUAL LENGTHS AND EQUAL THICKNESS, EXTENDING HORIZONTALLY AND BEING DISPOSED ON EDGE ONE ABOVE ANOTHER WITH THEIR JUXTAPOSED END EDGES DISPOSED IN PLANES WHICH ARE NORMAL TO THE SIDE FACES OF THE PLANKS, SAID EDGES BEING LOCATED ALL IN SOLELY TWO VERTICAL ROWS RESPECTIVELY AT THE TWO JUXTAPOSED END EDGES OF THE SETS, THE JUXTAPOSED END PORTIONS OF THE PLANKS OF THE SETS HAVING SEPARATE AND INDIVIDUAL KEYING MEANS COMPRISING FORMATIONS HAVING OPPOSITELY DISPOSED SLOPING SIDES, SAID KEYING MEANS BEING LOCATED AT THE SIDE FACES OF THE PLANKS, ALL PORTIONS OF SAID KEYING MEANS BEING SPACED INWARD AN APPRECIABLE DISTANCE FROM THE END EDGES OF THE PLANKS, SAID MEANS EXTENDING ENTIRELY FOR THE FULL WIDTHS OF THE SIDES OF THE PLANKS AND, IN EACH SET BEING IN ALIGNMENT, SAID ALIGNED KEYING MEANS OF THE SETS BEING LOCATED IN TWO VERTICAL, SPACED ROWS SPACED INWARD FROM THE END EDGES AND CHARACTERIZED BY SAID OPPOSITE SLOPING SIDES BEING IN ALIGNMENT AND CONTINUATIONS OF EACH OTHER,