The answer to this pussle is Tank G

dejt4u:

This is the direction of float of the liquid..
From tank A to B to C to J (it can't go to D because pipe leading to it is blocked).
Then from J to L (it can't easily get to pipe I because the liquid will need a high pressure to move up against gravity).
While it is struggling to gather enough pressure, the water level in tank J will be rising and the liquid will easily go through to tank L, then straight to F (since pipe leading to H is blocked).


Therefore, tank F will be filled first

You are a genius.