Why are two holes made to empty an oil tin?

$A$ tank is filled with a liquid of density $\rho$ up to a height $H$. The average pressure on the walls of the container is:

$A$ barometer is kept in an elevator accelerating downwards with an acceleration $a$. What is the most likely pressure reading inside the elevator?

$A$ container of height $10 \, cm$ is filled with water. There is a hole at the bottom. Find the pressure difference between points at the top and the bottom.

The figure shows a siphon. Choose the wrong statement: ($P_0 =$ atmospheric pressure)

If the pressure at half the depth of a lake is equal to $2/3$ of the pressure at the bottom of the lake,then what is the depth of the lake in $m$? (Assume atmospheric pressure $P_0 = 10^5 \ Pa$,density of water $\rho = 10^3 \ kg/m^3$,and $g = 10 \ m/s^2$)