[Don T]

Muriatic acid will take the rust out but you will find it only marginally effective if it has not been degreased prior; any type of degreaser will do. Do not breath the fumes, do not do it on concrete you want to keep, wear rubber gloves and old clothes, do not cause a splash. When the rust is gone you will have to dilute the acid, then neutralize then dry the tank. You will get flash rust but the sealer should take care of it. One qt will do a tank; you will have to roll the tank to place the sealer. You will have to figure out where to dump the cruddy contents/acid. It is not expensive but is a lot of dangerous time consuming work. I did my truck tank only because it was going to cost a gazillion $ shipping for a new one and I had the place to do it. It is still sealed after 6 years, was a Hirsh product. How long it will last I do not know. A rad shop will not likely be able to clean it well enough to apply the sealer. I suggest that if I had to do it again I would spend my children's inheritance and go for a new tank.