A cover (30) for inhibiting the outflow of fluid from an access port of a working channel of an endoscope, the cover comprising: an outer casing (32) that can be removed from the access port, the outer casing including an upper end , a lower end, an outer peripheral surface extending from the upper end to the lower end and an inner peripheral surface extending from the upper end to the lower end, the inner peripheral surface extending around a central longitudinal axis of the housing outer, further including the outer shell a coupling portion close to the lower end of the outer shell adapted for engagement with the cover of an endoscope； an elastic member (40), at least a portion of which is located internally with respect to the inner peripheral surface of the outer shell, the elastic member including an upper surface, a lower surface, an outer peripheral surface extending between the upper surface and lower surface and a central opening sized to admit an endoscopic instrument therethrough, the central opening having a circumferential surface extending between the upper surface and the lower surface of the elastic member, the elastic member also including a slit extending outward from the circumferential surface of the central opening towards the outer peripheral surface of the elastic member； and a guide wire blocking structure (60) formed by two tabs (62) in opposition to each other, each tongue extending from and above the upper end (34) of the outer shell forming an opening between the respective tongue and the end top of the outer shell, each opening sized to accommodate a guide wire between the tongue and the upper end of the outer shell.Una tapa (30) para inhibir la salida de fluido desde un puerto de acceso de un canal de trabajo de un endoscopio, comprendiendo la tapa: una carcasa (32) exterior que puede retirarse del puerto de acceso, incluyendo la carcasa exterior un extremo superior, un extremo inferior, una superficie periférica exterior que se extiend
