How to discard water quality volume to an arbitrary outfall?

Hi, 

I have a model in which a pond goes to an outlet structure to go directly to our storm system. However, we want to discard the water quality volume from that same pond to go to arbitrary outfall so it does not affect downstream of our system. I know what the volume that I need to discard is. 

Therefore, I was wondering if it would be as simple as having two outlet structures with pipe attached to each of them, one for the water quality volume and one for the rest of the flow? For the water quality volume the pipe after the outlet structure would end in an outfall. 

How would I make sure that only the amount of XXX of volume  is taken to that pipe? 

Thanks