How to convert to eyedropper
This is the practice of turning a pen with cartridge filler pen into an eyedropper one, suitably sealing the barrel threads with silicone grease or possibly inserting an o-ring to ensure effective sealing.
At the moment we do not think it is the case to document this practice, for the reasons that will be very clear if you continue reading, and it is rather the case to ask a question: but who makes you do it?
This is of no practical use (if you really need a lot of ink, take a box of cartridges with you), it exposes you to the risk of stains (on paper, not bad; where the pen loses you, a bit more problematic). For a more detailed examination, please refer to the article and the discussion mentioned in the references.