It's not real hard, any two ASAs can work but on-offs make life a lot easier, especially if one is a purging on-off (you don't want two). Basically you want the bottles close (less waste) and the 20oz upside-down.
Just make sure you pay attention to what you are doing, do not drop the setup while fililng it (you may want to do it low to the ground the first few times at least), and turn on and off the valves in the correct order.
I had a setup that had a non purging on-off ASA and an older remote style pin depressor, connected by a short piece of 1/8 brass pipe nipple. I would have loved that on-off to have been a purge type.
Last edited by drg; 07-29-2008 at 09:43 PM.