Ignoramus14003 wrote:

Even easier (and safer) would be to put down a hose from a compressor,

A compressor does not pump enough cubage. They are intended for pressure.

and let it pump air for a day, while at the same time trying to smell
the air coming out. I would think that if there is no perceptible
smell, including from an air sample from the bottom, there should not
be much risk of an explosion. But, better safe than sorry.

I get a numb nose and cannot smell anything after about the third whiff.
(No, not huffing. Gas mixed with 2-stroke smells different from straight
gas, and it's easy to get the cans mixed up after they've been sitting
for a few weeks.)