So I flushed the tank out again today, I have been using a gallon of Vinegar each time and sitting the tank up on one end, then the next time changing it to the other end etc, each time replacing the gallon of vinegar. This last week I had the tank upside down soaking the inside top of the tank. Each time i have done this I have washed out the rust scale that came off after draining the vinegar and each time there has been large amounts. If you have a look at the pic you will see what I mean. The vinegar doesn't dissolve the rust but makes it separate from the unrusted steel leaving a grey metal etched surface.
I am currently soaking the filler region of the tank but once that is done i will take some more internal pics for all to see how it went.
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