Ummmm....... it's not a "tube" that collects moisture and then sits still or stagnant. It's just a tap valve, with a ball bearing sort of thing keeping water back. When the metal tip is tapped, it moves the ball which lets water drip out. When the metal tip falls back straight, it blocks the water again. Every time the tip tilts, water escapes.
Nothing backs up anywhere.
Now, the waterer may get algae growing in it, which may occlude the movement of the valve. Or dirt and crud may fall into the waterer and block it, over time. Like all waterers, the components should be flushed now and then when they don't work correctly.