I chuck my tubes on a drill bit, and set them on my drill press. I just hold green scotchbrite against it while the press spins
You can slip your tube
through a drill bit wrapped with something, and put it on a electric drill. Than hold your sand paper against while trying to make an even brush
Heres a before and after (brass and steel tubes)
before
after
Heres after buffing with Simichrome polishing paste on the drill press with a car hand-buffing pad.
Here's a different before an after of brushing the matte finish of a Richman genny (with green scotcbrite)