Abstract: This invention provides a submersible self-priming dispenser of measured doses of toilet tank additive in which the additives are solid products which will dissolve in water. It dispenses a measured amount of the water soluble additive each time the tank is emptied. In the present invention, when the tank is full, air locks form to separate both the top and bottom openings of the dispenser from the tank and prevent the water-dissolved additive in the dispenser from mixing with the water in the tank. Dual chambered embodiments are also presented so that, if more than one additive is used, they may be kept in separate solutions between flushes.