unseats an outlet valve 28 the outward flow lowers the tank water level and float valve 16 opens to permit an inward flow somewhat less in flow rate than the outflow through the drain a portion of the inflow water is directed through a water line 32 into an overflow tube 34 in direct communication with toilet drain 24 to refill the bowl not shown after outlet valve 28 has reseated in response to a predetermined lower level generally near empty the flush tank water conditioning device 40 according to the present invention shown in fig2 comprises an insoluble support frame 42 having a downwardly extending elongate support leg 44 a mounting hanger member or hook 48 and a mixture or compound of one or more water soluble water conditioning agents 50 compressed onto leg 44 to form a downwardly extending soluble column insertable within the flow of water from line 32 into overflow tube 34 and sized to be dissolvably washed by this flow without materially interfering with the flow rate through the tube as shown in fig3 and 4 one embodiment of the support frame leg comprises orthogonal fins 52 extending along the elongate length of leg 44 to provide ample surface area for the compressed compound to adhere further the leg or fin surfaces can be dimpled or perforated to enhance adhesion a layer of water soluble dye 54 may be.