An assembly of two components configured to be in contact with hydrocarbons, and a fuel tank including the assembly. The assembly includes a casing or a retaining member fastened to the casing, each of the two components including at least one fastening part configured to interact, and at least one of the components being made from a material configured to swell through action of the hydrocarbons, thus reinforcing retention of the components on one another. A method for manufacturing such a tank includes assembling the two components in the absence of fuel, and then bringing the two components into contact with the fuel.