Having trawled through the internet i tried the viegar and salt mix so i filled it up , shook like crazy then left it on the bench. Next morning the tank had dumped the vinegar all over the floor but not from where i bunged the petcock hole

Where it had lifted crud from the tank it had deposited it around the tank so ive dne what i was with water and left it with wd40 to stop further rust prevention.
So what is the best way to clear the tank for use?
Im thinking diesel, shake loke crazy and drain maybe? Or just bite the bullet and get some por15 to line the tank but will this effect the line at the top of the tank?
I must admit throwing in the towel and buying a new tank has also crossed my mind