The Haro II is presumably a classic lever filler with internal rubber sac. To fill, the nib is dipped in the ink bottle, the side lever operated (compresses the ink sac) and then returned to the starting position; through the resulting vacuum the sac sucks up the ink. Replacement ink sacs are rare in Germany but still available in the USA from a specialised firm; an assortment with about 15 sacs in various sizes costs about 33 euros.