I just purchased a 10 gallon 135 max psi portable air tank at Sears, so
that I can fill and store it, then have a handy source to fill tires and
whatnot when I need to. Product webpage: http://tinyurl.com/6ys6u

Then I read the directions. It says "Always drain the tank of all air
after the last use for the day & before repairing or removing any
component parts." I imagine they're concerned about moisture which
could probably condense in the tank as the air decompresses, but maybe
it's just a concern that somebody could be hurt w/ the compressed air?
It does warn to disperse any accumulated moisture by draining to 25 psi
and then inverting it while draining the remaining pressure. .

Does anyone store air in these tanks for extended periods of time
(apparently that is more than one day)? Will I be alright if I drain
the tank every month or two and invert it so the moisture can come
out? If I can't use it to store compressed air in the garage, I might
as well return it.