Abstract: The fluid tank is divided by a planar partition (3) into a fluid inlet compartment and a fluid outlet compartment. Toward the outside, the fluid tank has an annular protruding rim (19) surrounding two openings (1, 2), one for each of the two compartments. A coupling device case en bloc including inlet and outlet pipes for the fluid, which are placed facing the openings (1, 2), is provided with centering means cooperating with the rim (19).