Can you tell which one will fill up first - water tank | with Answer

Can you tell which of the black plastic water tank will fill up first ? There are a total of 12 water tanks from 0 to 11. 

Answer

Tank number 7

Explanation

The connecting pipe from Tank 0 to 1, then from Tank 1 to 3 & from tank 3 to 7 is on the bottom of the upper tank. So as water enters the tank it immediately flows to next tank. But the connecting pipe from 7 to 10 is on upper side of tank 7. So only after filling tank 7, it flows to next tank 10.