Clean tar out of gas tank with NaOH

I have this Vanagon Syncro that didn't run for 31 years. The gasoline turned into thick black tar with about 5 gallons of liquid ontop. It's polymerization, it's like turning to plastic. It's horrible stuff. Acetone cuts it, and laquer thinner cuts a little better. Gasoline doesn't cut it at all. But NaOH (Lye, Sodium Hydroxide, Caustic Soda, in water) eats it up and makes it "Sodium Hydroxide" in the ingredients. Read the cautions on the label, they aren't kidding. It will dissolve your skin. I used 3 1/2 bottles for this project, about 5 pounds ($40).
It etches steel. I don't know if it's OK for a steel tank. I put a steel 'filler pipe' in the stuff and it ate all the rust off and made pinholes in the pipe wherever it was heavily rusted. I'd minimize the time steel sits in the NaOH.

[@DBCooper363]

Worked perfect 👍🏻

[@t_sodo8745]

Good to hear

[@juanka1053]

What is the brown stuff on the cup before you put the drain cleaned?

[@t_sodo8745]

That is tar. The gasoline was in the tank for 31 years. It polymerized into black tar in the bottom of the gas tank.

[@BP7BlackPearl]

where do u get this stuff?

[@t_sodo8745]

What stuff? Tar is gasoline after 31 years. NaOH is from the hardware store

[@azadaranda5634]

Wbu in a plastic gas tank

[@t_sodo8745]

yes it's a plastic gas tank