Hit the Extrude Dialog button, change Extrusion Type to Local Normal, set the Extrusion Height to -10 and hit OK.
Go to Edge mode. Select all edges (Ctrl+A). In the Top View deselect the middle row of vertical edges. In the Front View deselect the angled edges. Chamfer the selected edges 0.1 units. Can you guess what shape will have the smoothed object?
Well I can't tell you what this is but it looks nice and smooth and has a tubular middle. I guess you can imagine something this would resemble to.
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