Well it's nice of you to go to the effort of making a video, so thanks for that.
However, I would agree that the handle section is not where the black hand plague comes from. The waterfed poles we use all have fibre glass handles that don't produce the black dust. The dust comes from the carbon fibre sections wearing down as they are constantly extended/retracted and rub against the clamps as they go.
In my experience, the only good way to solve this problem is to take the pole apart, clean each section to remove any dust on there and then spray clear lacquer on each section. This works a treat.
The first time I did this I could not believe the difference it made. It was like a new pole.
You need to do this about every month.
Now I do this to all my poles on the first Friday of every month. Takes about 30 mins to do 1 pole.