If you've ever used KOH-I-NOOR Rapidograph Tech Pens size 3x0/.25 and smaller you know how temperamental they can be. I've just started using them again for certain things and finally feel like I've got a hold on the clogging issue. These pens are so damn expensive and unfortunately over the years I've bought the same pen multiple times. I figured maybe I could help someone out by writing my findings and eventual triumph. First of all, always use new-ish ink! If you've had the same ink sitting in a dusty back drawer don't expect it to work. It'll clog quickly and you'll end up chucking the pen across the room like a 2 year old. Secondly, if you are going to leave your pens sitting unused for over 2 days, clean them with the Pen Cleaner (It's probably just dish soap and water but it's really cheap and comes with a neat little plastic strainer thingy inside). It's a pain in the arse to clean them but so is buying a new 20 dollar pen. I haven't decided whether or not the Pen Cleaning Kit is worth it for regular maintenance but it is pretty good for trying to get super old pens working again. If you are inking over pencil lines use a harder lead pencil. The softer graphite is a big part of why the small pens get clogged so easily. Don't shake the pen violently at all. If it clogs while working, I personally keep a small piece of paper-towel dipped in pen cleaner nearby then I put the metal nib in the cleaner and bleed the ink out. Works fine for me. I saw a new pen on the market that claims to be clog-free...but I don't believe it.