I just got done cleaning a small gas tank on a small generator.
I did not want to suffer with getting foreign objects back out of the tank, so I got a bunch of 1/4" nuts, threaded a string through the holes to hold them together. I left plenty of slack in the loop of string so that they would act like they were loose. I shook it by hand and it cleaned up the crud very nicely. I reached in through the fill hole with wire with a small hook on the end and fished the nuts right out, and since a added a pint or so of paint thinner, they came out nice and clean!
A truck tank would require a lot more nuts and a better way of shaking it to clean it.
