Process for manufacturing a plastic fuel tank provided with at least one accessory (14) connected to the internal space of the tank via at least one orifice (12) in the wall (10) of the tank, the accessory including a projecting element (24) extending to the outside of the tank, the processing comprising the steps consisting in providing a film (22) that includes a peripheral region (28) and a border region (30) around an opening in the film, in placing the film on the wall of the tank and on the outer surface of the accessory in such a way that the projecting element passes through the film via the opening, in welding the film over its entire peripheral region to the wall of the tank, and in welding the film, over its entire border region, to the outer surface of the accessory.