I got my rods from FJ's and I remember you saying Norm that's where your rods came from.
Yes the safest way is to fill the empty bottle with water before cutting but I don't do that most of the time when
cutting up gas tanks etc ,I fill the empty bottle with compressed air a few times and empty and repeat until
the air coming out of the tank can not be ignited with a lighter .
The scrap yard here will take a complete gas tank so you don't have to cut them up.
I guess the bottles will eventually rust away in the ground just might take 100 years.
I did see an alloy bottle after it exploded and it took out a lawn mower

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Cheers
Max.