Cleaning a gas tank

The gas tank is not very large, so the technique I used for cleaning out a motorcycle gas tank may work. Empty gas tank and remove from car. Remove sending unit from tank. Put one or two pounds of small (grape size), rough gravel in the tank and seal the openings. Shake tank vigorously for three to five minutes. (If you want to get the tar like stuff out, add ½ gallon of diesel fuel with gravel.) After shaking, empty tank, and examine. If cleaning not complete, repeat.

Disposing of the diesel, rust, and gravel is a HazMat PITA. Back before responsible disposal became PC, I used to pour it out along fence lines where we didn't want grass or weeds to grow.