I just cleaned my diesel tank yesterday. I have had the boat less than 2 years so I was not sure what shape it was in. It is a small tank, about 14 usgal and I took it out which seemed the simplest. I also wanted a look at the bottom to see if there was amy corrosion, it is aluminium.
Pumped all of the diesel out and removed it. There was a lot of sludge and black scales on the bottom. We drained it through the
fuel level indicator hole.
We just rinsed some fresh diesel in it a couple of times and it looks pretty good. Mostly shiney and clean. I was going to use gas but the diesel worked.
Only one small spot of corrosion on the bottom and it is not too bad. I am going to coat the bottom with some thing, just not shure what yet.
Gary