jon,
you can always get a 4mm to 3mm festo reducer and use 4mm festo fuel line from the pump to the reducer to the turbine. Also, most of the time if the air is accumulating in the UAT, you have an air leak somewhere further down the system. this could be from a small pinhole in the lines or a "crimped" connection where the safety wire is on the tygon line. What i typically do when safety wiring the tygon onto the brass tubes is to make on complete 360* round and then another w/ the wires coming off at the same sides. That way the tygon is clamped onto the tube a full 360* and doesn't "crimp" an edge allowing an air bubble. I can't get a good visual of how the UAT is mounted, so pictures might be a good idea.

thomas