I successfully devalved a little propane tank today, the kind they don't
want you to use any more. I bled it off for a couple of days, with the
tank set at the top of a largish sloped driveway so the gas would run down
the hill and diffuse. When it finished hissing I turned it upside down with
the valve open for a few hours. Then I took it into the shop and plumbed an
air hose to it and pressurized it to 120psi and vented it, then repeated
the air venting twice. I tried to get the valve to admit water but it plain
didn't work. I cobbled up a chain clamp setup like Ted Edward's, heated the
threaded area with a handheld propane torch until the paint barely started
to smoke, and turned the valve out easily with a large crescent wrench.

It was a lot easier than I'd thought it would be based on all the horror
stories. I filled it with hot water and a little dishwashing detergent
for a first cut at de-stinking it (I don't much like the garlicky smell
of methyl mercaptan). If anyone has any bright ideas as to how best to
get the stink out of the tank I'd like to know about it.

I'm going to make a little forge.

Grant Erwin