Depending on the status of the pen and my impatience, this can be one of the following options:
1. Immediately fill with ink (from the bottle or refill the cartridge)
2. Rinse with water, wipe with a paper towel, shake (like a thermometer), let lie for about 5 minutes and then refill.
3. Take a toothbrush with a thin nap and detergent for dishes (without balm for the hands! Clean!). A drop of detergent on the toothbrush, grind it to form a smooth foam. Then brush my entire nib, feeder and accessible inner parts of the pen near the feeder, polishing like teeth.
Then, using the syringe, the inner canal channels are likewise washed (if possible).
Then all this is rinsed under pressure under running tap water, slightly warm, until the detergent is completely washed off and its traces.
Then, like in paragraph 2, we wipe it, shake it off, let it lie down. And then refueling.
p.s. The composition of the ink is very different. In some strong surfactants (similar to some special detergents) a lot. In others, there are none.
And a certain composition of the residues of substances in the channels of the pen or on its feeder or nib can cause precipitation of some substance from the ink that you fill up. In this case, the permeability of the channels and surfaces of the pen will be radically broken.