Tanks and cylinders. - Page 2

Here's what my yard has to say on their website.

IF YOU HAVE SOME INDUSTRIAL EXPERIENCE, AND YOU HAVE THE EQUIPMENT HERE'S HOW TO GET TIN PRICE FOR YOUR TANKS..... BUT ONLY IF YOU KNOW WHAT YOU'RE DOING. WE MEAN THIS, IF YOU DON'T KNOW WHAT YOU'RE DOING SCROLL BACK UP TO THE BIG BADDA BOOM PART OF THIS SECTION, CAUSE THAT'S WHAT CAN HAPPEN.

1. REMOVE THE VALVE ON TOP OF THE TANK

2. FILL THE TANK COMPLETELY WITH H20 .... WATER

3. PUNCH OR DRILL TWO HOLES IN THE BOTTOM OF YOUR TANK

4. LET THE WATER DRAIN OUT OF THE TWO HOLES

A hair dryer or heat gun can help with getting the valve off, its a real light weld you gotta break. If you can stick the tank handles through an iron bar cast in concrete or something like that to stop it from moving, then take a monkeywrench and a 6' cheater bar to break the weld.
I watched a video once in class where firefighters were trying to rescue a guy cleaning a 10 000 gallon empty benzene storage tank. He had been overcome by vapors inside, they took a demolition saw and tried cutting into the base of the tank while a hose with water was aimed at the cut. When they cut through BOOM two firefighters killed many injured. Tank was at atmospheric pressure-relative 0 PSI.
Seeing that wrote off cutting into non-purged tanks for me. There might not be oxygen in the can YET but once you puncture it there will be.

I would end up spending more in ammo than what I got back in scrap.