"Existential Angst" wrote in message
...

Given that a tank has already had some service, what would
you guys do to try to keep the spare tank available for as long
as possible?

Leave it full of water?

Drain it?

My thought was that draining it would be worse, because
allowing air in, it would rust.......
EA

I acquired a serviceable used electric water heater from a remodelling
project and mounted it horizontally in a close-fitted greenhouse box
as an unpressurized solar batch heater. After about 3-4 years the tank
started to spring small leaks on the cold bottom side which I patched
until I couldn't keep up.

Anything you put in it, like RV antifreeze, will be very tricky to
completely remove because the tanks are so hard to handle. The best
way I found was hanging it horizontal by a choker sling with the
heater holes on the bottom and spraying a hose in through them, but I
doubt I directly rinsed even half of the surface area and couldn't
touch anything absorbed into the crud in the vee groove around the
concave bottom end. Since the tank wasn't connected to my plumbing and
the water was only for laundry or car washing a little soap or LPS-3
in it didn't matter.

They can be difficult/expensive to dispose of unless you have a friend
in the scrap business. I traded two heaters for an old farm wagon
front axle.