Hi Frank

I take your point about LPG tanks, I'm so used to them I didn't think to add a warning to my post. The tank was empty then the brass valve broken off , then left with the hole down to drain. That was about 10 years ago, so I knew it was OK. I spent years cutting them in half at a scrapyard, OK if you know how.

It didn't occur to me to do as you said with the bung. I also wanted to have the fill/drain hole where I could reach it, so I could drain it to save weight at times.
I must have a bit of brain fade... of course water is heavier, any idiot knows oil floats!. I'll try to get better at explaining things in any posts.

Steve