So as I didn't have any 'spare' fuel to put in the tank - Guess what happened - the moisture of cleaning it made it a 'bit rusty' again - ARGHHHHHHHHHHHHHHH..... However, as I have plenty of fuel now (& also ACID - LOL) today was pleasant enough to redo it.. This time after washing the acid with 2 lots of water & Bicarbonate of soda to neutralise it then air drying it - from the compressor, I put in some Eastwood Metal Prep for 30mins. Then emptied that & filled it with fuel - IT LOOKS PERFECT !!!!!!!!!!!!!!!! Now put into the technical notes - GET the fuel before starting this process..