Gas tank messy black sludge

I am working on a 1963 Rambler that has been sitting for about 20 years. Every thing is done except the cleaning of the gas tank. It had about 10 gallons if nasty gas in it that will burn nicely in the oil burner. But it left behind a sticky tar like stuff. Any ideas on how it clean the tank? Thanks..

Call around and see if anyone will do it. Radiator shops used to boil out gas tanks but they might not anymore. All depends on what sort of chemicals the EPA allows shops to use anymore.

I've used the Eastwood 3 step kit before with good results on rare tanks. It uses strong detergent, acetone and muriatic acid to clean then a tough sealer. The acetone and muriatic come from your local hardware or home improvement store. A short length of chain can be added to the tank during the cleaning steps. Slosh it around and it will help remove the gunk.

I used the POR15 kit on the tank in my 65.It was totally nasty after sitting for about 15 years.That was back in about 98.It still looks new inside.You must follow the directions.I also let mine sit in the sun after each step.When I put the sealer in it sat for 2 days in the hot sun.Rocky

I used lacquer thinner and ball bearings in a truck plastic tank, It's the only thing I found (that I had) that worked to cut the gunk.

I'd price a new tank (if one is available). It might be time/money well spent to go that route. Might prevent future carb issues on down the line. That tanks' condition sounds real bad