Method for manufacturing a plastic fuel tank by moulding a parison in a mould, in which method the parison is locally deformed during moulding of the parison in order to obtain an impermeable hollow built-in connector provided with a screw thread, and to do so by means of a concave counter-form and a convex form that can penetrate the counter-form, these two pieces being secured, one to the mould and the other to a core located inside the mould, or vice versa, and at least one of these pieces being provided with a screw thread, the moulding of the connector taking place by the convex form penetrating the concave counter-form.