(1) When the perimeter of the bottom surface of the storage barrel is (260.2-9)cm and the radius of the bottom surface is 40cm, it cannot be put into the open space. At this time, the radius of the bottom surface can be 30cm (the excess part rolls into the interface). At this time, the volume of the storage barrel is 380.4 cubic decimeters.
(2) When the perimeter of the bottom surface of the storage tank is (134.6-9)cm and the radius of the bottom surface is 20cm, the open space can be put down. At this time, the volume of the storage tank is 326.8 cubic decimeters.
To sum up, the maximum volume of the storage barrel is 380.4 cubic decimeter.