This is a good opportunity for combining a curve with a screw modifier.
I start with a Bezier curve and edit it to the shape of the outer edge of the desired double funnel (hour glass):

The key features are to have the central control point exactly on one of the axis, and its handles parallel to the axis that forms a plane with the first axis. For the example, I picked the Y and X axis, respectively.
The distance along the Y axis sets the narrowest part of the curve.
Then I add a screw modifier:

Since I was lazy and left the Bezier curve on the XY plane and since I picked the Y axis for the center point, the screw should apply on the X axis:

Here's another view, after editing the curve:

The upside of this approach is that it can be very fast and it is non destructive. Only 3 control points and a modifier that you don't have to adjust once you've set it up.
The downside is that if you want symmetry you need to be careful in how you handle the two outside control points. They have to have the same Y coordinate and the X coordinate of one must be the negative of the X coordinate of the other.
But if you start with a curve that already has those properties that's easy enough to do.