This is an outstanding check valve! I used the valve that came with the TMC CO2 Regulator and Soleniod kit and had noticed the one day that water from the bubble counter managed to back flush into the regulator! Tips: 1) Make sure the bubble counter is not too closely placed to the regulator 2) Don't fill the bubble counter with more water than is needed. 3) Place one of these guys just after the regulator 4) Be paranoid like me and place another check valve just as the airline leaves the aquarium.