The invention relates to a discharge selector for water-closets, that allows the control of the discharge of water from the cistern of the water-closet into the bowl, in two different proportions, which allows less water to be used when liquids are to be removed from the bowl and a larger proportion of the content of the cistern to be discharged when solids are to be removed from the bowl. Said device consists of a single part provided with mechanisms that allow it to operate in the described manner and also allows the quantity of water discharged to be adjusted within a certain range. The device is universally applicable and does not leak water even if the packaging loses elasticity. The device can be installed by the user thereof as the installation is just as easy as that of the replacement flap in any currently commonly used discharge valve.