Device for the fluid-tight connection to a receptacle of an accessory of which the active proximal part is intended to be placed in communication with the inside of the receptacle by an opening in the receptacle, the device having an axis (1 a) and comprising: • a first means of generally tubular shape with a proximal end opening and a distal end opening, arranged to ensure the attachment of the device to the receptacle, to define a passageway between the inside and the outside of the receptacle, to form a support that guides the axial sliding of a second means between a closed distal state and an open proximal state along an axial stroke C, to participate in defining a chamber, • a second means, generally elongated, mounted axially in the first means, with an interposed lateral sealing component (39a, 39b), so as to be axially slidable along the stroke C between the closed distal state and the open proximal state, arranged to comprise a transverse head at its proximal end portion which is adapted, in the closed distal state, to close the opening in a fluid-tight manner, to contain a space having a proximal wall formed by the adjacent head, a distal boundary, and a side passage opening, to comprise at its distal end portion an axially slidable actuating part, and to form a support for the accessory so that its active part is positioned within said space, to participate in defining a chamber, • a chamber including said space and which, in the closed distal state, is closed off laterally by the first means and, where appropriate, is adapted to contain in a fluid-tight manner a liquid for preservation, adjustment, monitoring, or calibration of the accessory, and which, in the open proximal state, is freed of the first means and is thus able to be in communication with the inside by the side passage opening, characterized in that the first means comprises a proximal end portion for fixed assembly by sliding, arranged so as to be assembled in a fixed and fluid-tight manner, with an interposed lateral sealing component, to a complementary fixed assembly part of the receptacle, by means of at least an axial sliding in the proximal direction, • the transverse head has a peripheral lateral dimension and shape that fit with those of the inner surface of the first means, so as to be axially slidable within the first means in the proximal direction, from its distal opening to its proximal end portion, the head being fitted with a lateral sealing component such as a head seal, • the second means is adapted for pre-assembly to the first means by an axial sliding in the proximal direction, the accordingly pre-assembled first means and second means forming a structural whole adapted for assembly to said complementary assembly part by sliding axially in the proximal direction. • a first means of generally tubular shape with a proximal end opening and a distal end opening, arranged to ensure the attachment of the device to the receptacle, to define a passageway between the inside and the outside of the receptacle, to form a support that guides the axial sliding of a second means between a closed distal state and an open proximal state along an axial stroke C, to participate in defining a chamber, • a second means, generally elongated, mounted axially in the first means, with an interposed lateral sealing component (39a, 39b), so as to be axially slidable along the stroke C between the closed distal state and the open proximal state, arranged to comprise a transverse head at its proximal end portion which is adapted, in the closed distal state, to close the opening in a fluid-tight manner, to contain a space having a proximal wall formed by the adjacent head, a distal boundary, and a side passage opening, to comprise at its distal end portion an axially slidable actuating part, and to form a support for the accessory so that its active part is positioned within said space, to participate in defining a chamber, • a chamber including said space and which, in the closed distal state, is closed off laterally by the first means and, where appropriate, is adapted to contain in a fluid-tight manner a liquid for preservation, adjustment, monitoring, or calibration of the accessory, and which, in the open proximal state, is freed of the first means and is thus able to be in communication with the inside by the side passage opening, • the transverse head has a peripheral lateral dimension and shape that fit with those of the inner surface of the first means, so as to be axially slidable within the first means in the proximal direction, from its distal opening to its proximal end portion, the head being fitted with a lateral sealing component such as a head seal, • the second means is adapted for pre-assembly to the first means by an axial sliding in the proximal direction, the accordingly pre-assembled first means and second means forming a structural whole adapted for assembly to said complementary assembly part by sliding axially in the proximal direction.