Disassemble your pen. Unscrew the nib from the barrel of the pen, then gently twist the ink reservoir from the nib.
Take apart the nib. Thread the nib tool, a black plastic disk about the size of a penny with a square hole in the center that came with your Rapidograph, over the tip of the nib until the square hole fits around the square base of the nib. Rotate the nib tool counter-clockwise as the nib points at you until the two components of the nib separate.
Pour cleaning solution into a dish half filled with warm water, then submerge the nib pieces and the ink reservoir in the solution. Use equal parts cleaning solution and water.
Leave the pen parts in the solution for several hours or overnight, rinse them with warm water and allow them to air dry before you reconstruct the Rapidograph.