It sat for so long I am worried about what lurks in the tank? I have been using this one steady and know it's clean, the other I dumped some diesel additive in .. I just don't know and I'm skeeeered! Lol I'll just have to put 10 gallons in and see..
Unless you have some reason to be afraid, I would give it a try. If the fuel is waterlogged, pump it out and replace the fuel. But don't be afraid of something that hasn't done anything bad to you...

Filling it full will allow what is In there to blend in better.