Southwind Fuel Tank. Should i clean?

I am restoring a 81 Southwind and currently am addressing the fuel tank. I just siphoned out most of the gas. Its a 3o gallon tank and i pulled about 27-28 gallons out. PO stated he topped it off and added fuel stabilizer for last winterization. So the gas i pulled out was amber and clear until i hit some sludge layer and there was a significant amount. I looked inside with a flashlight and saw a clean aluminum bottom to the tank and a small about of debris and some fuel/sludge left.

The inside surface of the tank seems very clean. There is a little debris on the inside and quite a bit of green/white powdery buildup on the cap and the first part of the gas fill tube. Does this buildup tell me anything? And what is the best way to get rid of that last little bit of sludge?

I thought i pour in about 2 fresh gallons of gas and siphon that back out to get more of that sludge out. And what should i do about the corrosion? I cleaned the cap easily and it is very clean now but if i try to remove the buildup in the fill tube i risk some falling into the tank. but i did consider packing paper or shop towel in and cleaning then carefully pulling the towel out.

Here are some pics.