The nitrogen or argon should only be running through the bubbler when the line is actively in use; it should be turned off at the end of the day.
To avoid using nitrogen gas unnecessarily, ensure that the nitrogen line to the manifold is completely turned off. If the lines are sealed and the bubbler is set up properly, the manifold will contain the nitrogen gas and remain under an inert atmosphere. The line may be flushed before next use for up to 5 minutes if a leak is suspected.