I’m new to WetCanvas and watercolor, but this is what I know.
The Lamy Safari fountain pen is so popular because it’s sturdy, quite affordable and the nib is perfect for drawing.
There’re waterproof inks, which can be used with fountain pens for example De Atramentis Document ink, Platinum Carbon ink, some Iron Gall inks (made for FP), Sailor Nano inks aso.
You can also use water soluable inks to your advantage like for pen and ink, wetting parts of the ink for shading. There’re great artists (like Liz Steel or Jane Blundell), who use this technique.
I hope some more experienced artists will jump in.

Silas (Who loves and still writes/draws with fountain pens)
PS If you have further (in depth) questions regarding fps and inks, just ask.

I use a mix of both waterproof (De Atramentis Document Brown or Black) and water-soluble inks in my pens. The water-soluble inks are fun but are only really for sketchbook use – most dye-based inks for fountain pens are not lightfast at all and will fade even more rapidly than fugitive watercolor pigments! Still, some of them are very attractive for drawing – I like Lie de The by J. Herbin and Ancient Copper by Diamine. They are both water-soluble to different degrees. The De Atramentis Document inks however are very waterproof and lightfast – given a minute to dry they won’t move under watercolor at all.

With regards to pens, I also have a couple of Lamy Safaris – I find them reliable, tough, and smooth to use and the ability to easily swab nibs is handy. I also have a pair of Pilot Metropolitans – these are less expensive and also seemingly quite reliable though I haven’t had them as long. My one fancy fountain pen is a Platinum 3776 with a flexible nib that allows for nice line variation similar to (but not as extreme as) a dip pen. Overall I like to use fountain pens rather than something like a Pigma Micron just because I can use less pressure and still get a strong line on paper – being able to choose any ink I like is also a huge plus.

SilentW mentioned some artists who use water-soluble inks to their advantage – I’d add Marc Taro Holmes to this list.
https://citizensketcher.com/2014/06/09/washable-ink-at-the-botanical-garden/

Here’s one of my own attempts at using water-soluble ink. It uses Diamine Ancient Copper in a contour drawing where I melted the ink with a wet brush and some ultramarine blue watercolor.

None. I prefer watercolor as the primary and only medium when I paint.

Sling paint,
Virgil

I use a fountain pen with watersoluble ink when I have just enough time to go over the sketch with a water brush (to mark the values quickly). This would usually be while standing in the street chased by stray dogs, or on a train, or bus…

Big fan of Platinum Carbon ink here, and the Platinum EF fountain pen. It has a nib almost as sharp as a crow quill, minus the dipping, and I love me some needle-sharp pens! That model is made for use with the carbon ink, so it works well without clogging. At about $13 USD, it’s affordable too.

The EF pen is a desk pen, so it’s really long and the cap doesn’t post. I shortened the barrel with a Dremel tool and now the cap posts. The super-short barrel suits me very well – I like smaller pens and it fits well in my kit. Not a mod that would work for everyone, but it does for me.

Also have a Kuretake #40 brush pen in my kit, which is obviously not a fountain pen. I included it since it works in a similar way. It takes the same converter as the EF pen, and also works well with carbon ink.

These are my first decent fountain pens, other than some inexpensive Shaeffer models, so that’s the extent of my experience so far. I’d like to try the Noodler inks and a Lamy Safari in the future.

One thing I found about Carbon ink, it generally dries instantly (and waterproof-ly) but not always! If you really pour it on (especially if a pen burps or the brush pen slops) there will be a layer of carbon that doesn’t soak in, and that can smear later on. In normal use, this won’t happen. The other instance is if it just doesn’t get dry before you wet the line. I was sketching outdoors on a damp, foggy morning, and ended up ink-washing the stuff because it just refused to dry. Lovely effect really, though my paper must have been pretty soaked from fog/dew to have that happen with Carbon ink!

CK =)
I take great comfort in knowing that my genuine typos will probably be blamed on some device's autocorrect.
DIY art supplies, sketches, and more: cyntada.com / @cyntada

I love ink and wash for out-and-about sketching. I use a TWSBI Eco ($30 for a fairly indestructible piston-filled fountain pen) with Noodler’s ink in polar black, which is waterproof. The ink is interesting in that it was designed to be used in freezing temperatures while keeping the ink liquid (which typically isn’t an issue in the southeast US), but I’ve read that it’s also good for keeping a piston fountain pen functioning well. I liked Pilot Metropolitans when I first started out, but found that they tend to have problems with leaky nibs. Considered a Lamy Safari, as well, but I haven’t tried one out yet.

Just remember–don’t put shellac-based drawing inks into a fountain pen! Stick with the FP inks. (or you’ve lost your FP).