Abstract: The invention relates to an insert element 13 for inserting into the filler neck 10 of a tank suitable for filling with urea at a filling station by means of a pump nozzle 12. The insert element 13 comprises a cover element 24 with an opening having an inner diameter that is smaller than the outer diameter of a standard pump nozzle spout 12 for Diesel fuel, and support means for mounting the cover element 24 to substantially the plane of opening of the filler neck 10.