linda mar wrote ...

should I air-bubble it overnight? or just leave it sitting?

Either way, a couple of gallons should entirely outgas overnight,
particularly if you start with hot water.

waaa :-( too much hardware... my tank is essentially free-standing, so
more tubes will not be easily routed, not to mention not much floor space
left inside the tank...

Don't sweat it. A 2-liter juice bottle with an airline from the cap
straight to your powerhead, that's it. You can set the juice bottle on top
of the tank. We'll talk about it later. How big is the tank?