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This one had Dave, Falen and Steve-O stumped! Falen gave up without guessing; Dave had a few different theories; Steve-O guessed bucket 5. Which one do you think? See the answer below!
The answer is bucket 5!
Why?
There's a wall/stopper just to the left of bucket 5, meaning the water will not continue to flow down into bucket 2 and will back up into bucket 1