Okay the vinegar will work but remember to deactivate it with baking soda when you rinse but to do it appropriately there are few steps that are a little advanced but give the best possible results 1 reverse electrolysis that is putting a piece of rebar that's isolated in a tank of washing lime you put the positive on the tank and the negative on the rod I'm pretty sure look it up in the wiki that will draw all the rust to the piece of rebar then when that's done you rinse it out with a little bit of vinegar left in it overnight to clean it the rest of the wall washing lime out then when you rinse it the next time after it dries get denatured alcohol and rinse it make sure you get it on all the metal parts then you use your tank repair gel of your choice whatever fiberglass or epoxy based stuff they have on the market and it will stick but you got to have a thin coat on the inside and it has to be complete you have to get everywhere inside of it and even coat stick it in the sundry and y'all have a tank that will last another 30-40 years for a step through if you can find a really really cool radiator guy it's a rarity that you can find one of these guys but they recoat the inside of Radiators they can do a step through they could recoat it with bronze and fix the worst of Tanks it costs but if you're really into it it's worth it