Sometimes you want to prevent new clips from cluttering up your other collections.
Each collection has a "garbage avoidance" setting, which you can use to reject new clips - rejected clips go into the InBox. Right-click on a collection, select Properties, and then turn off the "accept new clips". They'll now "bounce" into the InBox.
If you have a bunch of collections, you can set them all quickly by dealing with the database directly. Go to Config | SQL Window, and erase the default query at the top of the window. Paste this in there:
update coll set acceptnewclips = false
where id > 1;
Re-start, and all collections except for the InBox, are now set to reject new clips.