Linux SCP defining destination port
Capital "P".
$ scp -P 12345 svn_backup.tgz user@xxx.xxx.xx.xxx:/path/to/new/svn/
See $ man scp
for more details.
It's also noteworthy that the port specification must come before the file name, i.e.:
scp svn_backup.tgz -P 12345 user@xxx.xxx.xx.xxx:/path/to/new/svn/
*won't work.