A process for manufacturing a fuel tank, including: inserting a plastic parison including two distinct parts into an open two-cavity mold; inserting a core inside the parison, the core including two parts of a reinforcing element capable of securing two different locations inside the parison; pressing the parison firmly against the mold cavities; fixing the two reinforcing element parts at the two locations of the parison using the core; withdrawing the core; closing the mold, bringing its two cavities together to grip the two parison parts around their periphery to weld them together; 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; opening the mold and extracting the tank; making an opening into the tank wall; and through the opening, putting at least a third reinforcing element part to link/connect the two first parts together.