I lived in New York City all summer long and my fountain pens came with me. I was there completing a post graduate certificate in typeface design, and what kind of type and letter-lover would I be without my trusty pens? The challenge for me was that I was living in a small, but beautiful, space with a roommate and working very, very long hours. I anticipated this reality before I left for the Big Apple, and found immediately that it would ring true. I'd likely be putting in some major time cleaning my pens after I got home.
And, I did.
After I got back, I did a deep clean of all my pen parts; even the caps and barrel bodies. I'm lucky that I had no major gunk or crust anywhere in sight.
I soak (in plain water) all of my plastic-bodies pens (like LAMY Safaris, for example.) My vintage and antique pens I do not soak, and I would suggest the same to you. Metal pens can survive a soaking, but you need to really make sure the pen is thoroughly dry. I soak my newer model metal pens, but it's usually a quick soak.
For my convertors, I fill and empty with water 5 or 6 times. Then, I fill with water and let sit. Every few minutes I'll literally shake them a bit. Ten or so minutes later, I fill-refill with water several times.
You really truly should do this until the water runs clear. Depending on the ink you are using, it may seem like it's taking an eternity to clean the ink out.