We've got an ancient RV (25 years old) and I sanitized the system when we bought it about 7 years ago. The vent hose was a clear plastic line from the tank to the air escape on the fill-up hatch. That clear plastic line was green as it was fully of mold/algae. I took a small bristle brush and ran it through the hose (after removing it) and that did the trick to clean it out.
But even after sanitizing, we only drink bottled water in the RV. We only use the on-board water for showers, toilet, and dish washing.
Well, I've probably rinsed my tooth brush with it a time or two. :)
Steve