To mount a pump on a small-mouth bottle by providing a sleeve to be mounted on a reinforced head part of the small-mouth bottle to seal a connection part.
A lower part 1b of a sleeve 1 is integrally formed with a tubular upper part 1a, is coaxial and flush with an external tubular element 10 of the upper part 1a. The lower part 1b is constrained to an underlip of a reinforced head part 3 of a small-mouth bottle by a metallic retainer cover 5 fitted elastically in a mouth part 4 of the head part 3 thereof. A pump 2 assembled in advance and the sleeve 1 on which the metallic cover 5 is put are mounted on the small-mouth bottle quickly in one operation when a force is applied in the axial direction. At mounting and operation, the lower part 1b of the sleeve 1 is elastically deformed in the outward direction, particularly in a part of facing 15. Since the facing 15 exists there, elasticity of the lower part 1b is improved on the whole. Here, the sleeve has high elasticity and can return, even if it is equally bent in the outward direction over whole outer periphery.