1st pic: after sweeping, one end of tube is not horizontal. I tried a few times and apparently I can do that by adjusting the curve. Is there any guidelines to make it perfect?
2nd: No closed loop after rotating, which means I can’t extrude the face. I didn’t see the principle behind that. Two planars share the same axis that still make them independent faces. By zooming in, seperated points can be seen but it didn’t allow me to fix.