The configuration line in make.conf to rsync (example):
/etc/portage/make.conf
SYNC="rsync://rsync.us.gentoo.org/gentoo-portage"
will be isolated in a configuration file repos.conf with the following content (example):
/etc/portage/repos.conf
[DEFAULT]
main-repo = gentoo
[gentoo]
location = /usr/portage
sync-type = rsync
sync-uri = rsync://rsync.us.gentoo.org/gentoo-portage
auto-sync = yes