The present relates to a method of manufacturing a product by the steps of i) injecting a sufficiently heated thermoplastic material into a 1st cavity to form a preliminary product comprising a collar having a connecting feature located on the inner surface thereof, then ii) optionally cooling the preliminary product of step i), then iii) blow molding the preliminary product in a 2nd cavity to form a void volume, wherein steps i) to iii) are performed in a single molding unit, then iv) removing the finished product produced in step iii) from the single molding unit.