Karl Townsend writes:

Any good ideas to rid an
old bottle of propane smell?

The advice others are giving about bleach alone is ineffective. Typically
the stinkum is bound up in greasy petroleum goo stuck inside the tank.
You'll need a non-polar solvent to get that out with rinsing and, if you
can get inside, mechanical scrubbing. Then you oxidize any residue, such
as with heat/air or pH-lowered bulk dilute chlorine bleach. Tough to reach
everywhere to get the last detectible odor out.