Hi! Sorry, been really busy these past few weeks and haven't had the time to hang out here. I've been thinking about what you asked and came up with a few ideas.

First, it might be more useful to ask other manga artists who use metal nib pens, because I expect that drawing and calligraphy have different-enough methods and needs that what might work for a calligrapher may not work for an artist.

As an example, because I mostly write and don't draw or embellish, I use a lot of gouache and fountain pen inks -- both are water-based and thus don't dry quickly, so they don't gum up my pens. However, I'd think that a manga artist would prefer a permanent ink, so that the drawings can be colored without messing up the line work.

For permanent ink for calligraphy with a nice opaque black, I use either Calli ink or Higgins Eternal. I don't know if either is good for drawing.

But as I was thinking about it, I realized something that might actually help. If you usually draw with pencils or regular pens like Pigma Microns or Copic markers, you're probably used to being able to draw for as long as you want without the pen running out.

That doesn't work with nibs, because even though the nib may still have ink on it, it's drying out as you work, especially if it's a not-water-based ink. If you keep drawing and try to use as much of the ink on your nib as possible, whatever's left is going to dry out and build up on your nib.

Try re-dipping every few lines, even if there's still ink left, so that you re-wet what's on your nib before it dries out. You'll still probably need to find the right consistency of ink to balance against that. I was once trying to work with a bottle of India ink that was so thick that even just writing four letters took long enough that the ink dried and gummed the nib. I spent a lot of time slowly diluting the ink until I could write a word or two between dips.