Abstract: A method of grinding an inner surface of a tank that includes convex first and second parts joined by a cylindrical part, the together defining an inner surface, the method including providing a frame for holding the tank and a stand rotatably connected to the frame. Initially, the frame assumes a horizontal position, and an amount of grinding material is placed into the tank covering a part of the inner surface of the tank. Thereafter, the tank is rotated about a central axis, causing the grinding material to move in a sliding and non-tumbling movement relative to the inner surface. The rotation is repeated in a first tilted position and in a second tilted position, wherein the grinding material extends on the inner surface between the cylindrical part and the respective points of interception between the first and second parts and the central axis of the tank.