You can add a parallel reference plane to one of the standard planes passing though the center of the tube. On the Command bar, pick the center point option from the drop-down.
A couple of ways I can think of -
If the ends are perpendicular to the axis, create a plane on the end, then a plane at 90° to that one.
Tangent plane on the cylinder, then a parallel plane offset to centre of cylinder (in ordered) or just move it if in sync (you can also rotate it in sync)
I'm not sure of your situation, but I would take a step back and ask, how was the tube created? If it's a sync part, the origin can be moved so that an axis of the origin can be your center line. If the part is ordered, it would need to be created on the center line of the tube.
In general, I would try to get the center of the tube on the center of the coordinate system of that tube part. Then the coordinate system becomes the axis you desire.
If your tubes are already mated using it's own coordinate system, then this could cause problems.