As with ink cartridges, fill your flux pen when it becomes dry.
- Drill a small hole in the barrel of the flux pen (top end).
- Puts about 2-3ml of liquid flux into a syringe, thin if necessary with IPA.
- Empty the syringe into the hole you drilled.
- Cover the hole with a piece of Scotch tape.
This also works with watermelon and a distilled beverage.