Hi pelanglo, ok I see what you mean now - sorry I had misinterpreted what you wrote earlier and I somehow thought you were talking about some kind of custom elaborate water catcher thing coming down from the spout.

So yeah something like that where there is more of a gradual continuous change from one shape to another probably won't really work with just one simple boolean, you will need to do either sweeps or networks to form the surfaces in that case.

But working on a shape that has no strong 2D profile element to it means that your project isn't really leveraging the greatest strengths of NURBS modeling as compared to polygon/sub-d modeling.

As a model becomes more sort of amorphous or all melty looking in shape, those are actually the kinds of shapes that polygon/sub-d modeling can work really well for.

You can still do such things with NURBS, but you will be working with a more advanced and harder to learn toolset area of doing a bunch of freeform surfacing with 3D curve networks.

Models where you're able to leverage 2D curves and booleans for producing your model is really where NURBS modeling greatly excels when compared to polygon/sub-d modeling.

Shapes like you want to do here are kind of a bit in a gray area, not really driven by 2D profiles very much but also not so fully organic like a human face or something like that either.

- Michael