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Well, assuming the pipe going to 2 is blocked (like it looks) then 5 will fill first
Otherwise 2

Correct! Congratulations, you have a good observatoon skills. I upvoted you.

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I believe number 3.

Cool puzzle, be sure to give us the answer! My guess is number 2

Of course, I will tell you the correct answer a bit later :) I didn't hit first time too.

Correct answer is given by @taimur.
Thanks all you guys for participation!