It's a pretty cool setup really. The grease travels back through center of the spindle and then moves through the rear bearing, into the hub cavity and out through the front bearing. If the grease is very old or contaminated I would not rely on forcing it all out with a grease gun...best to tear down, replace bearings/ races/ seals with fresh grease. Then you will keep the grease fresh with routine maintenance. Also I believe it requires a DOUBLE LIP INNER SEAL, so be sure to get the correct one!