The destination out blend mode is excellent for creating a tool such as an eraser in a drawing app. I looked at the construct demo capx but I couldn't figure out why my eraser was a black square instead of doing what it was supposed to do. However, after a bit of fiddling around, this is how I solved the problem:
Click on your layers (on the bottom right side of the screen) and then in the layer properties menu (on the left side of the screen) make sure that the Force own texture is ticked. That's it! Hope it helps :-)