These two huge plastic barrels, which I assumed were empty? Not empty. Left was half full, right is full, although some of it is likely water. An empty can of šprotas doesn't make the best fuel cap
I stopped filtering when I ran out of clean jerrycans to fill. With the tractor tank also filled to the brim, that's 120 liters recovered so far.
Won't have to buy tractor fuel anytime soon!