A limited flush retrofit control device for toilet tanks is useable on both ball valve tanks and flapper valve tanks. A U-shaped horizontal thrust member with vertical arms attached to each side acts to effect closing of a ball valve or flapper valve as its up-or-down motion is controlled in a desired path by horizontal guide means attached to the tank overflow pipe and engaging the vertical arms of the U-shaped thrust member. Each vertical arm is fitted with a float, adjusting clips and preferably with weights. The adjustable clips determine the heights of the float on the vertical arm. The flush volume prior to reseating the ball valve or flush valve by the thrust member is a function of the position of the floats on the vertical arms. A full flush is effected by maintaining the tank lever arm in the flush position until the tank is emptied.
