Fuel Tank Rust remove

Can anyone advise as to how or what to use to clean the rust from the onside of the Fuel Tank (removed).
I would prefer to use the Liquid method, rather than the Electrolysis method.
All help welcome.
I am presently trying to get my ST70 (1976)running and into a saleable State.

Plain white, cheap and cheerful vinegar works, Get a big bottle from Lidl or somewhere like that.

http://m.youtube.com/watch?v=Udn4BrKVlzw

Yep, i would second that. Get the cheapest you can, whack it in and i was told it would need a week but mine was like new after 4 days. It does immediately start flash rusting when you rinse it out, so either quickly swill around a cup of diesel or neutralise the acid like i did with a quick rinse round with a solution of this stuff.

Thanks for your reply.
I assume that after the Cider Vinegar has done it's job, it is then emptied out, the tank filled with water, and Soda added?
Is this correct? -- How much Soda do you use, and for how long does it stay in the tank?

It starts flash rusting as soon as the vinager comes out, have the soda mix ready. The strength of the mix is on the packet. Tip the vinegar out and straight in with the soda mix and fully swill the inside, this neutralises the acid of the vinager. I then kept pouring the soda mix through one of my wifes stockings to strain out the rust debris and kept putting the clean mix back in, swilling around and doing the same again till all the debris was out. It was then left indoors upside down over night to fully dry then petrol back in and away.
Basically you want petrol back in it as soon as possible. If you had an airline you could blow it out and use it straight away after the soda.

Its a great cheap easy repair.

Thanks once again, I will give it a whirl.
I can't resist it, - but I hope your wife was not wearing the stocking's at the time !!!!!