It can be a problem after many (thousands) of rounds. Pipe cleaner is about the best you can do for field cleaning. You could drop the entire upper into a solvent bath if you are back home from the range. I have put several thousand rounds through several gas system AR’s and have yet to have to take one apart to clean the gas system or even have to solvent bath one. But it could come to that if it gets dirty enough.
Saw super long pipe cleaners for sale somewhere intended for the gas tube.
Always thought of it as self cleaning anyway. Military seems to think that way.