Should I drain my CO2 tank before storing?

Working with CO2 tanks for aquariums: with long term storage, it depends on the pressure test date on the bottle, but I would probably bleed it out.

 

Not sure what you're trying to accomplish and/or prevent. CO2 doesn't stale and it's not going to cause the tank to corrode. There's no need to empty the tank.

FWIW, my 20# tanks last 2+ years each before before refilling. 8 months is a piece of cake. Consider, also, that many beers are aged, carbonated, in the bottle for years. Some for decades (some of those intentionally! )

 

Chemistry is the subject to answer this question and no . . . draining is not required. Carbon dioxide is a non-reactive gas with solids*. Your CO2 tank is aluminum or steel which will shrug off CO2 forever. Standard practice with compressed gas cylinders is to keep a positive pressure, this eliminates any nasty old moisture that's floating around in the air to enter. So the tank is actually kept in better condition with CO2 under pressure than ambient air.

Carbon dioxide tanks are essentially never emptied. Even when low, they are typically re-filled continuously over their 5 year hydrostatic cycle. About the only thing that can damage a cylinder like this is moisture (oxidation) or metal fatigue.

*CO2 does react to some burning metals like magnesium . . . so when playing with magnesium flares I would do it downwind of the tank.