COOL hubs refilling question?

I think I read every topic on this sight about these,anyways I have two questions, I have a 2001 Ranger trail with the big sight glass COOL.
Question #1. As I drain them the sight glass seems to suck in as the oil drains,I`ve read that they are spring loaded? When you refill the hub is it supposed to come back out or does it stay in?
Question #2. How much oil? I`ve read,fill them til the sight glass is completely full,this still allows room for more oil back at the fill plug.
I have also read fill them to the bottom threads on the fill plug,because you don`t want any air in them,which is it?

Thanks http://www.bassboatcentral.com/smileys/thumbsup2.gif

If the site glass is sticking out, it's over filled, this usually will not cause any problems. The site glass is spring loaded so when hub gets hot, the oil will expand and the site glass will stick out, it should go back down when it cools down.

No air....fill to the bottom of the threads. If the piston starts to pressurize, don't worry about it. The piston will move as the oil expands and contracts.