Never tried this....but.....a tow truck driver I know...his dad ran a repair shop for years and years was into AD trucks....he told me put Pea Gravel...you know....the kind they put on the roads after the oil? Put pea gravel in the tank and agitate....Gotta use the bigger rocks that won't stay in the tank....Knocks all of the varnish and rust off.
Here in MN, small washed river rock pea gravel is quite common...not sure what they have in TX.
