That's a pretty small tank,......If round, I'd lash up a set of casters, or improvised rollers,.....so I could spin the thing a bit. Throw in a bit of 3/4 crushed and do just ,....spin it,....
Big Towns have "Tank Cleaning" Service companies, on smaller tanks they go in with a rotary wand / sand washer,.....
Gravel or Sand Wash,....you're really just trying to get the BIG CHUNKS of crud, scale, rust, etc.......Your Filter Separator will Deal with the small stuff ,.....IF you are using the right setup,.....Mines a common NAPA #,....let me know if you need the #.
I've been treating my Diesel with "Sea Foam",.....so far , so good.
SHADE your tank, if at all possible, The combination of moist climates (yours) and heat grows bacteria in the BEST of Diesel Fuels.
Luck.
GTC
