vermaccio,

This question has been posted several times in forum. See for example an old one
http://forums.coade.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=1400&page=1
which hasn't a clear conclusion.

But I have also a question for you: you are focused on weight of fluid column, however what about the pressure of fluid? Are you ready to accept fluid exerts pressure on pump nozzle but no weight effects on it?

Maybe you would find my question as non-trivial because fluid height can be converted as pressure at flange level....