Foud a few mentions of using Vinegar as a rust converter in steel fuel tanks.
Has anyone done this and if so how did it go?
I use vinegar water to convert rust on light steal, rub down surface rusted panels and similar but have not considered the fuel tank until now.
I've got the tank out of the Notch and will take the sender out today, drop in some chain and a few nuts and give it a rattle around. Looks pretty clean inside but the mesh filter was pretty cruddy and choked. The filler inlet seams to have the worst rust.

Timely question, since I'm plotting and scheming to do mine too before dropping it back in.
Dunno about vinegar Mr Wombat, but I do know something that is absolutely guaranteed to work with removing rust..........on old extractors anyway!

My son-in-law got hold of 20L of molasses from a horsey joint and filled 1/2 a 44, then dropped in his rusty old pipes off his old Datto.
Came back home off-swing 3 weeks later, and they looked as shiny as new! I had heard that the stuff worked, but until I saw it in steel it was difficult to imagine just how effective the stuff is.

Oh, and I'm unsure if he used it straight or cut with water, a G@@gle-Fu would tell you I spose.

9 litres water, 1 litre molasses. Works brilliant but you have to treat the metal as soon as you wash it off. Give it a coat of wd40 or something to stop it from re oxidising.
Was hoping I could clean the tank this week and back in asap. Watched a couple of videos using vinegar then rinsing. I'm mosty worried it will etch the tank too much.
This is a good video for the Molasses Trick
https://youtu.be/KZCFcxf5IBw 

Vinegar is mostly diluted acetic acid, so it would attack the metal as any other acid would. People have tried using Coke as well - it's also acetic acid but a lot more dilute than vinegar, which is around 20%. I don't think acetic acid would 'convert' the rust at all - just slowly dissolve the steel underneath.

Rust converters also have acids in them, but usually phosphoric acid or tannic acid. These change the iron oxide to ferric phosphate or ferric tannate, which are more stable and basically inert.

That's similar to what I was thinking Phil.
I think its more for etching the rust off the surface as they say to neutralise the tank after rinsing with baking soda (bicarb) then rinsing with demineralised water to flush all the chemicals before reusing the tank.
Would rust converter form a stable enough coating after treating a tank and would it need to be flushed to stop the process?
I've used rust converter on floor pans to stabilise them. Leaves a nice hard grey/black oat of ferric phosphate that lasts ages even when pinted over. Would that layer last in the tank with no covering and would our modern unleaded fuel chemistry affect it?

I'd be trying to seal the insides once its been cleaned, rust converted, neutralised, rinsed and dried. Maybe some POR-15 thinned down and sloshed around inside, then left to drain and dry? Obviously you'd need the tank out of the car so it can be shaken, rotated and turned over as required.

Home made electroplating cleans and coats your tank
google it there is a couple of ideas