C'mon guys, you forgot the old stir the dome with the brake club technique. You do not always have to bash the sand pipe when a few judicious plunges and swirls with the club will do the trick. However, as you will recall, the brake club method does not work so well with a full dome or when the sand looks and feels like the tide just went out.
Oh yeah, almost forgot the jabbing the wire in the pipe method. Great for totally desperate situations. Makes you think you are doing something productive when nothing else works......are we in the station yet? I need a brew.....
BTW, at one time I thought the George sander was really an animated hood ornament.