Flexible tank having ring part

A filling method for a flexible tank for carrying liquid or liquid-based material, stored in the flexible tank, in a vehicle chassis or in a container, wherein the flexible tank has a body and at least one ring part, wherein the body defines a closed volume, and the at least one ring part narrows a cross-section of the body and forms at least one first compartment and at least one second compartment, wherein the filling method comprises steps of:

• engaging at least one ring part onto the body of the flexible tank in a manner defining the at least one first compartment and the at least one second compartment at two sides of the ring part before filling of the flexible tank,
• approaching first folding lines to each other which are defined at a first distance with respect to the ring part at both sides of the ring part,
• folding at least one folding region, which remains between the first folding lines, onto or under at least one of the first compartment and the second compartment, and
• filling a material, which is to be carried, into the body through the filling inlet.