Mainly at @dom14 and @mudski as they have rb30's, but maybe the same across other models.

The yellow cap that screws onto the overflow bottle. Is there a hose that runs from the inside of the cap, down to the bottom inside the overflow bottle?

I always seem to be missing about 30ml of coolant. Never more, even after a full weekend of driving. Thinking the system is warming up, pressurising as it should, rad cap relieves pressure to overflow, but when cooling down its sucking air back in instead of coolant (as there is no hose from the overflow cap to overflow coolant). I can't see how the yellow section of the cap is long enough to reach the coolant without a hose.

Am I right that I'm missing a hose here, or have I lost the plot?