an upstanding water reservoir 12 filled with water 16 to a water height a conventional float activated inlet valve can be used to refill the tank the upper portion 18 of the reservoir 12 includes an opening capped by a reservoir cover 20 which rests on a rim 22 the latter being simply the upper end 18 of the walls of the reservoir 12 the reservoir 12 is positioned at the rear of the toilet 10 and has in its bottom wall an opening 24 communicating with a bowl structure 26 of the toilet 10 so as to pass water 16 from the reservoir 12 through channels internal to the bowl structure in the usual fashion bowl rim 28 includes a plurality of ports which communicate the water 16 into the bowl 30 to provide for a flushing of the toilet 10 as is well understood in the art the opening 24 between the reservoir 12 and the bowl structure 26 is normally closed by an elastomeric flapper valve 32 hinged about a pivot point 34 shown in fig3 c to move between a closed state obstructing the opening 24 and preventing water flow therethrough and an open state removed upward from the opening 24 to allow the flow of water through that opening as will be described in detail below typically the flapper valve 32 is somewhat buoyant in the water 16 but held in the closed position when the reservoir 12 is filled with water 16 by the differential force.