Where are backup work files stored?

So, when I do a backup of a virtual system, and, the backup destination is another host via ftp, it appears that Cloudmin stores the file locally before transferring, is that correct. If so, what directory? I need to make sure I have enough space for some 1TB systems.

Was hoping it would actually stream the backup, is there any method that allows this and uses no work space?

To answer my own question, I found (when I ran out of space) they are stored in the webmin temp directory which can be changed in Webmin.

HOWEVER, I still wonder if a backup can be created via streaming only, without storing it locally via some backup method?