This device for closing an opening includes a frame (4) that delimits a pass-through access opening (10) suitable for receiving a cover (6) and which includes a frame hinge knuckle (18). The frame hinge knuckle (18) includes a hinge surface (38) and a pass-through hinge knuckle opening (40). The frame (4) has an exterior side and an interior side. The device also includes an inserted plug (52) positioned in a recess (50) of the frame hinge knuckle (18) located on the inner side of the hinge surface (38) and which makes the inner side of the frame hinge knuckle (18) appreciably sealed off from the outside.