To prevent some of hot water poured into a small bag from flowing along the side edge of the small bag into the terminal end of a groove positioned on the point of the corner of a container.

An assembly 1 is provided with at least one outlet opening disposed in the bottom. Further, the bottom is provided with many channel-like grooves 14 extending to the outlet opening in the radial direction of the inner space. The grooves 14 respectively have a bottom inclined downward to the outlet opening. Each bottom of the groove 14 has an angle substantially equal to 85 to the vertical direction. Further, the grooves 14 respectively have a rectangular cross section. However, it is not always rectangular, but any other shape may be accepted. Each groove 14 is extended from the position 18 separated from the side wall toward the outlet opening. The total area occupied by the grooves 14 is smaller than the total area of the bottom not occupied by the grooves 14. The case is provided with twelve grooves 14, and the adjacent grooves make an angle β of about 30°.