To send trains to portal :
Name the Portal first - Then at the top of your screen a little white form next to the quick drive , in surveyor , edit the driver rule for the desired loco giving it a route to follow or just from where it stands to the name of your portal - save and try in quick drive that it does what you want.
Portal to portal - only the trains that are in that portal or the portal has to be able to return trains after ' time ' , you specify that when you place the portal.
Hope that helps.
Steve