gas tank cleaning...

Had a gas tank that had a bunch of black greasy looking thick goo inside. I think someone sabotaged the car (previous owner) by dumping tar or such in the gas tank. I had bought the car cheap since it no longer ran.
Mixed up a 50/50 mix of industrial strength restaurant kitchen degreaser diluted with water. Filled the tank, then let is sit a week, stirred once a day. Rinsed with water several times, let air dry in the sun. The tank came out spotless, even the original fuel sender unit and inlet mesh screen were near new looking.
Had to cut out/replace the first several feet of the fuel line from the tank because it was clogged too.
The tanks been in the car close to 10 years now. The car runs great with no issues.