Rinfish, I think Nordic is right don't expect a Yeast system to be as controllable as a pressurised system, just settle down to a consistent mixture that is slow and steady. You could add an empty tank to the system as the extra volume will reduce the pressure variations caused by the varying rates of CO2 production. One thing is absolutely certain, DON'T put a valve in the system and shut it down over night. The rise in pressure in a small volume system is a real risk. Bottles can and do explode and you sure don't want that! The second reason is that the wildly fluctuating pressures day to night will make setting the restrictor valve a nightmare, but I think you found that already.