a method for manufacturing a plastic fuel tank including : a ) inserting a plastic parison including two distinct parts into an open two - cavity mold ; b ) inserting a core , bearing at least part of a reinforcing element configured to create a link between the two parison parts , inside the parison ; c ) pressing the parison firmly against the mold cavities , for example by blowing through the core and / or creating suction behind the cavities ; d ) fixing the part of the reinforcing element to at least one of the parison parts using the core ; e ) withdrawing the core ; f ) closing the mold , bringing its two cavities together to grip the two parison parts around their periphery to weld them together ; g ) injecting a pressurized fluid into the mold and / or creating a vacuum behind the mold cavities to press the parison firmly against the mold cavities ; and h ) opening the mold and extracting the tank .