Abstract: A passive dosing dispenser for issuing, for example, a predetermined volume of a liquid toilet tank additive solution into a toilet tank as the water is draining therefrom while the toilet is flushing. The dispenser employs no moving parts, and acts in response to the lowering of the water level in the toilet tank to dispense the liquid solution at a point in the flush cycle when it can be most effectively utilized. The liquid solution in the dispenser is maintained in an isolated condition by means of airlocks from the toilet tank water surrounding the dispenser regardless of the depth to which the dispenser is immersed in the tank during quiescent periods intermediate flush cycles.