The best approach is to use a converter to flush clean water through the pen. Use warm (but not hot) water. You can add a drop or two of dishwashing liquid if you are really anal, but that may not be necessary.
My approach is to fill a glass with warm water. Using a converter, expel any liquid in the pen into the sink, then dip the pen into the glass of water and draw up a converter full of water. Expel that into the sink, and repeat the process until the water that comes out of the pen is clear. If you do this right, the color of the water in the glass won't change. More that likely, however, you will see a faint discoloration in the water in the glass, so periodically dump the glass and refill it with fresh water.
Then, wipe the nib with paper towel, and let everything dry.