Can you be more specific?
You can also make a plane from 3D sketch. Just make e.g. 2 lines where you want the plane and make the plane from the lines.
You could make a plane from the temporary axis of the tube and one of the sharp points. No new sketches needed. This is assuming that the sharp points are centered on the tube.
If they are not then you could make a 3D sketch with one line connecting the two points, then a second line perpendicular to the first and parallel to the axis. Then make the plane with the two points and the end of your second line.
I used the second option you gave and successfully created the two perpendicular planes that are aligned with the copes to trim the points off. FYI: the two sharp points should be centered on the tube, but when I tried to use them to make a plane I could only select one, the other didn't appear to have a snap point.