I don't know wich is the easiest way to draw your tube but i can tell you how i would do it.I would create a sketch on the plane you used for the section and draw the axis of the tube you want to create.After that if you work in GSD use the sweep command(Profile type-->Cylinder...
Hi.
I don't think that both,US and metric units,can be displayed at the same time.If you want to change the unit dimensions(Ex:From US to metric)access Tools/Options/General/Parameters and Measure/Units.