A connector system for releasably securing a reservoir to a spray gun includes hook members on a lid of the reservoir that engage a flange of an inlet adaptor on the spray gun with a push/twist action to secure the reservoir to the spray gun. A retainer clip mounted on the inlet adaptor is movable between an inoperative position to allow the reservoir to be connected to and disconnected from the spray gun, and an operative position in which the clip blocks release of the reservoir. The clip provides security against accidental release of the reservoir in use of the spray gun.