Gas Queastion

For all of you that have had PWC's for a long time, how long is it before gas going bad is a consideration? I have been advised by techs from 2 weeks to 6 months. Fuel Stabilizers/Conditioners say that they can extend the storage time up to a year. Also with that in mind, if you are in the off season and may not be using your PWC for a few months or more, should you store with the gas tank full or empty or does it matter? A tech told me today that they empty the tanks when they winterize their PWC's. When I owned a boat, I was told to store the boat with the tank full because with less than a full tank, there is more chance for condensation and moisture getting in the tank.
What is your experience?

Also is it ok to run the engine out of water if you have the engine flushing hose attached and running water thru the engine?

Thanks in advance for any input!