A mouth piece assembly includes a mouth piece unit having a pivot which is pivotably connected to a first connector so that the mouth piece unit is pivotable about an axis of the pivot relative to the first connector. The first connector is pivotably inserted into a second connector so that the first connector is pivotable about an axis of the second connector. The two respective axes are perpendicular to each other. A locking key is connected to the second connector and engaged with the first connector inserted into the second connector. The mouth piece unit can be pivoted in two different directions and the volume of liquid sucked from the container is not changed.