Question

water does not run out of a dropper unless its rubber bulb is pressed

Answer 1

The pressure in the dropper is equal to the pressure outside the dropper(atm pressure).But as we press the rubber bulb presssure inside increases.Thus it flows from high to low pressure nd it comes out..(sorry in short)

Answer 2

It is because the pressure inside is less than the atmospheric pressure outside the tube.Therefore an additional pressure is required to make water run out of the tube of the dropper.