It is not obvious but the rsync --help
rsync --help|grep port
--port=PORT specify double-colon alternate port number
--port does not do anything at all actually for some strange reason it still uses 22
You have to specify a manual ssh command to make it work:
-e 'ssh -p 2210'
The snippet above is what you add for port 2210 change it to whatever port you need.
Full Example Below of Rsync using an alternative port number:
rsync -Phaz -e 'ssh -p 2210' /somedir/ firstname.lastname@example.org:/someremotedir