No need to clean the gas tube. It's a self-cleaning part and you are more likely to have to replace a gas tube because a pipe cleaner is stuck in it than because it's plugged =)
The part you refer to is the "Carrier Key" and doesn't really (under most circumstances) require cleaning. You _can_ use a worn bore brush to loosen some of the carbon in there, however, if you wish. I wouldn't go past the bend in it, though, or you're sure to do damage or get the brush stuck.