Interesting question. I can add files to that folder when logged onto
the server. My id is actually the same on both the client and the server.

The default path is specified in rsync.conf on the server. I want it to
be a large USB connected hard drive on the server.

I have been unable to chmod the permissions for the directory on the USB
device.

I've been doing some searching around and it looks like I may have to
add an entry in /etc/fstab to set that up properly (still reading about
that).