Everything(Tools | Options | Indexes -> Index folder size [if that is not a default?])
Most basically:
folder: size:0
I use, a lot:
childfoldercount:>=0 size:0 parents:2
adjusting the setting of parents:, which finds the
top most "empty" (including 0-byte files) directory trees, 2 (the parents setting) levels deep.
So: C:\TMP\ (& subdirectories thereof) or C:\OUT\ ...
Do verify that the selected trees
are empty by doing an Alt+Enter on the particular directories.
A setting of parents:6 finds:
E:\Users\therube\AppData\Local\Temp\SAL458.tmp
&
E:\Windows\System32\Tasks\Microsoft\Windows\RemovalTools
(The latter is not something you would want to remove.
IOW some directores are expected to be there, even if empty.)