So redirect the output of the tee to a subshell, that's one I totally missed. Argh. A subshell is definitely needed?
I was reading things that were swapping, or is that duplicating, file descriptors like: 3>&2 2>&1 1>&3. If tee didn't exist, is it possible?
Using cat is a bad habit that keeps creeping. Redirection, pipes, file descriptors, subshells and their environment, is something I'm working on getting better at.
Thanks all.