Greasing Hubs on 2003 2720sl

I went and bought a full size grease gun and the appropriate grease today and started pumping grease into my hubs (they have a small metal cap not a rubber cap if that helps) to this point I have put over 1 full tube of grease into the drivers side hub and have seen NO old grease come out???? I'm wondering if it is going up into my brake drum or if it was just completely empty????? Any help or ideas would be appreciated, I tried searching and didn't really come up with anything
Thanks,
pat