Homebrew PCBs

I got three or four ml of solder powder and ground rosin in the mail.
 According to the manufacturer, the rosin is all right for
electronics, but that it should be cleaned off for long term use.  I
think it will be ok for prototypes, but I guess we'll see.  I'm
working on making a Epson color 400 into a flat bed.  I've got it
chopped up, but I need to track down the 'paper is present' switch, as
it keeps bitching that it's out of paper and won't print, though it
feeds paper, card stock and circuit board OK.  Of course, I have not
gotten it to print, so the head may hit the board.  I'll take it with
me while I travel and beat it up some more.  
I've not refilled Epsons before, is it just an issue of putting ink in
through the feed hole at the bottom, or is there some other trick to
keeping it from running out of the air-hole, like taping the air hole
shut until the cartridge is installed?
Thanks
Richard