Correia,
I have always used a pipe cleaner to remove carbon from the inside of the tube. I'd dip the pipecleaner in CLP, and run it in and out a number of times to scrub the crud (carbon) loose. Then dry pipe cleaners until there weren't any traces of the black left on them. This was a long and drawn out process. Now, the Armories have parts cleaning tanks with solvents like PD680 in them, and Citri-clean which we are directed to immerse the weapons in and scrub them. Obviously, the gas tube gets its fair share of the cleaner into it. Drying via compressed air and then pipe cleaners seems to remove a large quantity of the crud out of the tube. This is the 'accepted' cleaning method that the Marine Corps Air Wing's use.
When I was shooting matches more regularly, I'd use Brake Cleaner (Tricloro-triflouro- ethane) squirted down the tube and any other places where carbon was likely to hide, and then follow up with Acetone to wipe off the 'Trike' residue. NOT the perscribed method, but a fast and GOOD alternative. What the armourer didn't see, didn't hurt him!
But DO clean that tube, and DO NOT remove it! It isn't required! Remember, "This is my Rifle! There are many like it, but this is my own!...
Good Luck! Unkel Gilbey