Sorry for the poor picture but this collar controls the level in the tubes.
This is a pic of the dam inside the collar, as you can see twisting this collar alters the hight of liquid inside the tube.
Feed from pump into top tube.
Empty res showing brown pipe return, and the pump with bypass fitted.
And with the res full and the water returning from the vert.
Looking into the flooded tube.
And finally wrapped in reflective material ready to load up!.