Outflow object

[PavelBlend]

You need to create a new type of object that removes particles of fluid.
Something like a sink in the bathroom.
That is, those particles that fall into the volume of an Outflow object should be removed.
And the Outflow object should be created from a polygonal 3D model.

[doyubkim]

Simply erasing particles should be straight forward. For grid-based simulations may require sink velocity. I think we can put the particle remover first, and then add grid-specific out-flow later.