"Corky Scott" wrote:
I've been parking
my airplane under a shelter within a mile of Mobile Bay for five years.
I never top up the tanks after a flight. In that time, I don't recall
ever sumping a drop of water out of any of the drains. My tanks hold 32
gal. usable each.

That would be Mobile Bay Alabama, right? How much change in
temperature occurs overnight during the summers there?

16-20 deg. F. It falls to the dewpoint most mornings in summer.

Here in New
England, we can, and often do, see a 30 to 40 degree swing from the
cold of night to the warmest part of the day.

Overnight dry bulb temperatures, assuming no weather change, typically do not
fall below the dewpoint because of the heat of condensation. Therefore, if
there is that much swing, the dewpoint is mighty low; there is damned little
moisture in the air to begin with. Fuel tank respiration/condensation would
still not be a problem.
--
Dan
C-172RG at BFM