Stuff you will need to clean:

Hot Water

Koh-I-Noor Rapido-Eze Pen Cleaning Solution
Some people use alchohol or windex (yes, some people have recommended using windex.) to clean their pens, but I would not recommend it. The Rapido-Eze Cleaning Solution is cheap, works great, and you don't need to use that much unless you've got a pen that's been sitting at the bottom of an art supply box for over a year with dried ink flaking off. If your pen has that much dried ink, hell, don't even use any water, just use all cleaning solution and let the flaked out pen sit in the there overnight. For the most part though, you'll just need to use a little bit of the cleaner solution with hot water (add as much cleaner as you think you need depending on how dried/clogged up your pen is).

Last, but not least, is your pen.

Step 1:

The pen has several different parts. The first part you want to remove is the pen body. Start unscrewing the pen tip area, casing, and ink container from the colored part (Clamp Ring). Unscrew the pen body and set aside.

Step 2:

Take your pen tip tool which looks like a small black gear. Put the pen tip/nib key over the top on the tip/nib where the little color band is near the top, and just turn until the pen tip/nob comes off it's casing.

In the photo above are the four main pieces all seperated.

Now I am going to go completely against popular wisdom and recommend NOT removing the cleaning pin (the tiny piece of metal sticking out of the end that the ink flows from) & clear plastic bottom. Eveyone says you have to remove these two parts from the tip/nib, but I think this is a bad, bad, bad idea. More often than not, you will bend or break this tiny piece of metal and then you're out 30 bucks. So my advise, leave these pieces in tact and save yourself some money.

Step 3:

Next, pour as much cleaning solution as you think you need into the hot water.

Step 4:

Put the Rapidograph tip/nib, it's casing, and the ink cartridge into the water/cleanser and let it sit there for a length of time based on how dirty/clogged up it is. I let my pen sit for about 15 mins (the last time I used this pen was one month ago. It was a little clogged up, but not bad)

Step 5:

After letting the parts sit in the water and cleaning solution, rinse throughly with water and sit them on a paper towel to dry. Your're done! Ok, ok...I get that it's a pain to clean these rapidograph pens, but, they're worth the time to clean and maintain. They'll last a lot longer and give you better line quality in the end.

Here are some drawing I created using my rapidograph pens:
Civil War Soldier
Creek Drawing
Morgan Webb from G4TV