[MikeK]

Originally Posted by Bob Johnson

Here is the setup that I use. . . Bob

Bob, is the bottom of the milk jug open, or does it have a hole in it? If the jug is closed on the bottom and simply inverted after filling there is no way to equalize the atmospheric pressure above the jug contents.

Due to the extreme flexibility of that blow-molded container the pressure could be either more or less than atmospheric, adding or subtracting from the desired vertical gravitational head pressure.