Get a vertical cylinder, extrude both of it's top surfaces, scale these new faces down and make sure they're flat with the cylinder's surfaces, then extrude again and scale them on the y by 0.0000001 so they're flush flat in the centre, then delete the centre faces. You'll have a hollow tube.
If you want a tube with a one-sided hollow, just extrude one top surface, scale it down and extrude downwards to the required depth.