Question

A tank with liquid, above which is the air, has a hole in the upper lid, which is tightly closed with a stopper. Why after some time does the liquid stop leaking if you open a valve, located at the bottom of the tank? What should be done to ensure the free flow of fluid?

Answer 1

The flow stops when the pressure of the water column is balanced by the atmospheric pressure ρgh = Pa. To ensure the free flow, you need either to open the hole, or tilt the tank (to reduce h).