Cartridge filler (3)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">cartridge filler</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ink that I've seen before include "See 9" , "Liquid used to write" , "Liquid used in printing" , "Fluid from cuttlefish" , "Liquid in pens" .)