Can you post a picture of your reactor? It's a little tough to visualize what you are talking about. With a picture, I'm sure someone will be able to help you.

With the internal reactor, the rigid CO2 tube comes in at the top close to a side -- it goes all the way to the bottom of the viewtainer where it bends slightly so the CO2 bubbles come up near the middle. That CO2 bubble should be coming out of the rigid tube right near the bottom of the viewtainer.

What's tough for me to visualize is how the venturi loop can cause any pressure on the CO2 tube? Venturis suck in excess air, they wouldn't cause pressure.