The present invention relates to a method for manufacturing a tank (1) comprising a main body (4) with several compartments (7), a base (6) closing the lower part of the main body (4), and a cover (5) closing the upper part of the main body (4), said method comprising the following steps: shaping sheets to produce the parts making up the tank (1); assembling each of the component parts by butt welding in order to produce the tank (1).