Not really a nice topic, but quite usefull when speaking of Revit Families.
I´m repeating myself, from a post at the AUGI forums - But if you want a child/nested Revit family to cut a hole in the parrent/main family, like when placing a sink in a countertop, you´ll need to follow these instructions:
A: Sink family
1. New family, using the Generic FaceBased template....
2. Change the new family to the Plumbing Fixtures Category, (and share it)
3. Model the sink, and create a void, to representate the hole in the countertop.
4. Use "Cut Geometry" to cut the "Face" from the template, with the new void.
5. Save to library as desired.
B: Countertop family.
1. New family, using the Casework template...
2. Model the countertop as needed.
3. Load the above sink family, and place it on your new countertop face
4. Save again, and have fun :-)
And then again - we could take it one step further... when the sink is placed in the countertop family, pick it, and add a label to it, now you´ll be able to switch the sink famlily and/or type from within the countertop family, even when loaded into a project.