1. We can drink water from a glass using a 10 m straw (because of the atmospheric pressure acting on the water surface in the glass), right?

2. then if we suck air at one end of an U-tube manometer, the other end being exposed to atmospheric Pressure, we can only suck air to produce a pressure difference of 1/10th of an atmosphere, that is, 1 m of hydrostatic pressure.

In both the cases, the other end is kept open to atmospheric Pressure.. then why is this difference occuring?