Ok. So I made this set up tonight. The water can't overflow back into the CO2 system unless the cap is off the system. The co2 is forced to go out the only exsit: the end of the bottle cap.I'd think you would have to make sure the pressure of the co2 coming out was good enough to keep the water from being pushed into the tube by the powerhead. Is it possible to put it near the powerhead intake? Maybe I'm just being too cautious. Great idea and nice sketch.