Writing instruments with cork seals should be stored permanently moist, ideally filled with distilled water to avoid limescale deposits. Storage can be lying flat; with piston fillers also upright, but with the nib up, so that the seal remains wetted; the feed does not have to be kept moist. With fountain pens with rubber sac, it is recommended to remove the sac and only renew it when needed, since the plasticiser can cause discolouration on the material. Independent repairs should be avoided; defective seals are best renewed by specialists.