Since they are fuel tankers, I am sure that they are stainless. That makes a difference in how they are washed.
A few words of advice. The white streaks might not be due to a bad rinse. It could be due to hard water. Use soft water at the least, and I prefer Deionized water. It really helps on the polished stuff. If you do not know what it is, do a search.
As for the polished, the first thing that you want is to make sure that they are cool. If they are hot, the water, and chems will dry to quickly, and be a mother to get off, it will also damage the finish.
A lot of the guys here really like to two step, and it has it's place, but it doesn't have a place with these tankers. Brush 'em. That is the only way that you are going to get them 100% clean. I put a guy on top on the cat walk, and a guy on the ground to brush the devil out of them. If you try to get by without the guy on top, they will have a line all the way around them.
I am always the odd man out on these kind of things, and a lot depends on your location.
The big key here is DI water, I can guarantee that will remove any water streaks that the tanks may have. The biggest thing is rinsing them.
Of course, as always, this is my opinion, but I only wash about 50 of them a week.
Scott Stone