Take the tank boot off
Tank boots are designed to protect the bottom of the tank from scratches and dings. Since steel scuba tanks have rounded bottoms, a tank boot is also necessary if you want to stand the cylinder upright. Unfortunately, tank boots can also cause problems. They can trap water and/or salt against the surface of the tank, and accelerate corrosion. On top of that, the boot does a good job of hiding any rusting that’s already underway.
Take a look at these pictures of an old steel 72. This tank had recently passed it’s hydro static tests, but I noticed something when inspecting the outside of the tank: it looked like the tank boot hadn’t been removed in a while.
Do you see the corrosion that was hidden beneath the boot? That’s not good.
Had this gone unnoticed and the tank kept going diving, it’s possible that the continued rusting would have cause the cylinder to fail before it’s next hydrostatic test.
Your best bet is to remove the tank boots before your rinse your gear at the end of the dive day. Allow the tank and boot to dry separately, and re-install the boot for storage only after everything is dry!