Change FTP port in Backup.

[Buzzen]

In admin backup function, a user must enter the Ftp-Server, Path, Username and Password but there is no option to modify the port.

I want to backup to a server on a private port.

I have tried many formats but only receive this error "The name of the FTP server contains invalid characters."

Question is, how do I change the default port in the backup function to connect to the port our secure server is listening on??