Process for fastening an accessory to a hollow body obtained by moulding a molten plastic parison, this fastening taking place by snap-riveting with the aid of a tool during the actual moulding of the parison, according to which, before carrying out the snap-riveting, the parison is locally deformed so as to surround the snap-riveting zone with a dome (or relief that is concave when seen from the outside of the tank and convex when seen from the inside), the snap-riveting zone being also in relief (hollow) compared to the rest of the accessory.