Cleaning diesel storage tank

Just bought a 270 gallon diesel fuel tank from a oil company that I plan to put off road diesel in at the shop. What is the best way to clean the sludge from an old tank? Doesn't look terrible on the bottom from what I can see, but I still want to clean it out the best I can. I thought about strapping it to a trailer and driving it around with it 1/3 of the way full of half water with a heavy dose of purple power? Then several clean out cycles of just water. Letting it sit in my shop for a few weeks to evaporate what water is left in the tank.

Any suggestions? I do plan to run a water separator filter setup on the tank .

I have bought a few old tanks over the years and what I have found works the best is to get them flipped upside down and get a pressure washer out with a purple power water mix and go to town. Make sure you are in old clothes, because you are never getting that smell out.

If you just try to drive around it will not break the sledge up, and just hosing it out with water and no pressure will not clean it, I wasted 500 gallons of on road diesel fuel this way, not a cheap lesson but I will never make that mistake again.

Do you put the purple power in and let it sit for a while or inject it in with the pressure washer?

My buddy that restores cars will sometimes put a piece of chain in a gas tank to slide around and knock out any gunk.

Inject it with the pressure washer.

My luck went from bad to worse. While trying to remove the already broken brass drain valve it broke. Leaving me with just about nothing to get it loose. I tried using an easy out and all it did was make a larger hole. I almost feel like I have a chance to more or less carve the old brass fitting out of the steel tanks threads.

What size threads? Might have to drill it out all the way and retap.

I believe just from sight it looks to be 1/2"

If you can not get it to come out just cut it out and weld in a new bung. Circulating fresh air and/or water will keep the tank from going boom.