That is nasty looking!
I have a new fuel pump coming tomorrow, i hope it is correct, the rock auto fuel cap that came yesterday wasn't. The fuel lines have been flushed with carb cleaner, and surprisingly there wasn't that much crud that came out, although that smell of 25 year old fuel is enough to make a guy gag. I drained that out of the fuel tank, and the half gallon that came out didn't even light when i threw it on the fire out back.
Fingers crossed that this will start and run decent, i think that will keep my sons interest going once they hear it run, and can move it around the yard under its own power.
How did you deal with your fuel tank?