... edit your "servers" configuration file to indicate which proxy to use. The files location depends on your operating system. On Linux or Unix it is located in the directory "~/.subversion". On Windows it is in "%APPDATA%\Subversion". (Try "echo %APPDATA%", note this is a hidden directory.)
For me this involved uncommenting and setting the following lines:
If you are on Windows, you can also write http-proxy- options to Windows Registry. It's pretty handy if you need to apply proxy settings in Active Directory environment via Group Policy Objects.