speed of efflux

[suffian]

Consider a large tank open to the air with a small opening near its bottom. Consider water flowing out of this tank through the opening. Why must the pressure near the surface and near the bottom be equal to atmopheric pressure?

As fluid elements travel down the tank, they will be accelerating. Therefore I don't see how one could apply the rule of thumb that the pressure between two interfaces should be equal.

[suffian]

i think i got the idea. the pressure at the surface isn't equal to atmospheric pressure. But it doesn't matter because it is the pressure of the air that is pertinent in bernoulli's equation since the eq uses the pressure applied at the front and rear of the flow tube by its surroundings (which need not be another fluid element).

right?