Abstract: A weight and spring assisted actuating assembly for pressuring, with air, a liquid in a tank includes a reciprocating piston that is freely movable with a charging compartment. Appropriate manipulation of the charging compartment or, if applicable, the housing within which it is disposed, results in movement of the piston and causes outside air to enter the charging compartment and, subsequently, to exhaust into the tank to thereby pressurize the contents thereof. In accordance with an especially advantageous application of the actuating assembly, an air pressurized toy water gun is realized by ejecting air from the charging compartment into the water containing tank of the water gun.