There are 11
comments:

Male
1,806

depends.. if the water is coming out of the tap faster than the pipe in box 1 can drop it into box 2, then box 1 would go first. But assuming that's not the case, then obviously box 3 would go just before box 4, and box 3 would continue overflowing more than box 4.

Female
3,282

the whole thing would make a neat water bong :D (a dick to clean tho)

Male
55

Ok, I'm a super nerd, but by applying Bernoulli's equation, we can actually calculate the water level (head) difference of the two tanks to be:
h = (Q / A)^2 / (2 * g)
Where Q is the flow rate between the tanks and where A is the cross sectional area of the connector.
Just throwing some real numbers at this equation for people who don't like equations. Say we have a A = 1.6 square inches (about the size of a quarter), and that Q = 20 gallons per minute (about the speed that your bathtub fills at). The water level in tank #3 will be ~3 inches higher than in tank 4. Also, if you account for friction losses, this height difference will actually be even greater.
P.S., you should give us an option to edit/delete our previous posts!

Male
37,052

Welcome to IAB Tatung42! We moved formats a while ago, now we have no paragraphs, italics, smileys, or other useful things. We can put http links in luckily! And pictures sometimes work...

Male
55

Um...there isn't enough information to solve the problem?
But if we assume that the fluid flow is friction-free and assume that the flow rate into container #1 is less than the flow rate between the containers, then #3 and #4 will fill up at exactly the same time.

Male
3,590

We actually did this experiment in school. And you're right a little more information is needed it all comes down to where is the full line. Everyone was able to prove that their hypothesis was correct even though they got different answers changing the interpretation of the word full

Male
55

Nevermind. #3 overflows a fraction of a second before #4, see my post above :-).

Male
37,052

3 or 4 would fill up at almost the same time. I guess 3 would beat 4 by a couple of seconds (due to friction) depending how fast the water was flowing... so I concur with casaledana :-)

Male
55

Actually even assuming no friction, the only way for water to actually flow from 3 to 4 is if the water level in tank3 is higher than tank4. So you are right that 3 would overflow slightly earlier. You can even see this in the answer video posted (#3 overflows a fraction of a second before #4).

Male
37,052

Oh, it really does depend on the water flow: if it's 10x as fast as those connecting pipes can transfer it? Then #1 would fill up first, eh? So... 3 if it's really slow, and 1 if it's super-fast! :->

Male
1,135

easily answered if you remember water always seeks its own height, tank three

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