Why does bottle with long straw get emptied first? Two identical bottles with different straw length are filled with identical liquids (obviously up to the same height as depicted in the picture). Bottle with long straw is emptied first.What can be it's possible reason?

 A: In a fluid like water or air, the pressure $P$ and velocity $v$ depend on the height $h$ and density $\rho$ in a way described as the Bernoulli equation,
$$
P + \frac12 \rho v^2 + \rho g h = \text{constant}
$$
In your setup, the opening of the straw and the upper liquid surface at the base of the bottle are both open to the air, whose pressure doesn't really change over the size of the apparatus (that is, $\rho_\text{air} g \Delta h \ll \rho_\text{water} g \Delta h$).  If the straw is narrow enough that you can neglect the motion of the fluid at the top surface, $v_\text{top}\ll v_\text{bottom}$, this gives
$$
\frac12 \rho v_\text{bottom}^2 = \rho g (h_\text{top} - h_\text{bottom})
$$
The draining time is proportional to the mass flow rate $v$, so you can drain a container about twice as fast if you quadruple the length of the vertical drainpipe underneath it.
(Modulo the usual assumptions about how turbulence is hard, approximations are approximate, et cetera.  This is an engineer's approach.)
