Disposal of old propane cannisters?

[ericlp]

if they are the 4 gallon ones (regular bbq) type you could sell them for about 10 bucks on craigslist. Or give them away. As long as they aren't too rusty. I saw a sign at Pahoa bat/propane said they wouldn't fill tanks older than 5 years old. Don't know how they determine that. Probably a just a way out to not fill tanks that are rusty.