How much water for an inline system

I need your guys help on how much water I should be putting into an inline system. Last week I put too much in and luckily when I had my mobo in, it did not get hit when the fill line backed up on me Remind me to never try watercooling a desktop, thank goodness for side mounted mobos in towers . Should I just keep going till I see no bubbles, because it seems it can always take more even though you do not see any. Or is there a good measurment of water I can use? Any suggestions are appreciated.

I guess I don't really see how your fill line managed to back up on you, unless you just put too much water in it. I would fill it all the way (cover the fill line till it's flowing if it backed up when you started it) and then after a couple days add some more water (the air takes a long time to completely get out, unless you assemble it underwater....even still, there's the chance that some air is stuck in a corner or something...) and keep doing that until the fill line doesn't get a lower water level anymore.