I was reading on another forum where a guy is using an old 500-gallon propane tank as a hot water storage tank. That sounds to me like the perfect alternative to more expensive storage solutions. But since I have no idea what a used tank like that would cost, assuming you could find one, I'm just guessing that it's cheaper than some of the alternatives. Does anybody have any idea what tanks like that go for? I'm assuming they can take 30 psi.