A washing-agent dispenser designed for being mounted at a through opening (A) of a tub wall (5) of a dishwasher comprises:—a dispenser body (11), having a rear part (11′) and a front part (11″); —a perimetral gasket (30) mounted in a corresponding seat (S) of the dispenser body (11) and prearranged for exerting a sealing action with respect to a mounting side (5a) of the tub wall (5); —a frame (40) having a substantially annular shape, defining a central passage (B) through which the rear part (11′) of the dispenser body (11) is insertable. The frame (40) has at least one of the following:—first coupling means (41), which can be coupled to corresponding second coupling means (16) provided in the dispenser body (11), the first coupling means (41) and the second coupling means (16) being configured for fixing of the dispenser body (11) at the through opening (A) of the tub wall (5), in a condition of at least partial compression of the perimetral gasket (30) for exerting thereby a sealing action between the dispenser body (11) and the mounting side (5a) of the tub wall (5); and—reinforcement means (42, 43), prearranged for countering possible deformation or yielding of the tub wall (5) at least in an area thereof that circumscribes the corresponding through opening (A).