I have a 280 gallon diesel tank that has rust in the bottom I've drained the tank and took a magnet and got alot out of it but still has some what would be my best option to clean it out before refilling with fresh fuel
Pressure washer if you can reach enough of it. Otherwise add a couple of inches of water or diesel, and some sharp 3/4" crushed stone and let a teenager drive it around in the back of his truck for a while. A cement mixer works nice for smaller tanks, but that's a little big. Is this a round tank, or rectangular? that might make a difference too. The suck bucket is the tool to have to get the last of the gravel, rust, etc. from the bottom if the tank doesn't drain completely.
After you get it clean as possible, mount a fuel filter base on the pump and a spin on fuel filter, the bigger the better 'cause I doubt you'll ever get it completely clean. Mike
Thinking about what Delmer wrote, Maybe a pressure washer hose with a spray tip and a big hardened nut on the end. Leave enough length of hose inside the tank that the hose can flail all around the inside, and let it go for a couple of days...