QUOTE(Pete @ Apr 15 2008, 11:58 AM) [snapback]578432[/snapback]
I'm assuming you mean the pressure bar that you use to fill the pen? When the pen is full, you should get a good squirt of ink on the first press holding the nib downwards, then less and less will come out as you keep pressing the bar. 51s dont give up their ink easily, and they aren't a pen very well suited for changing inks frequently. By that I mean writing a page or two then clearing the pen and changing inks.
To really flush it you just immerse the nib in water and keep pressing the bar until the pen expels clear water. It can take a while. After that either rest the nib in some paper towels or snap it with your wrist till all the waters out. If you're patient its not a bad idea to let it air dry a bit after that so you don't get any water in your ink, but its not absolutely necessary.
When I clean my 51s, I flush them with water until there's no more ink, then I wrap the nib end with a paper towel or wc paper and shake it like a thermometer; be careful, a 51 can go through a wet piece of paper.