Storage Building: individual output control

Currantly I can control how much is stored and when to send product to production for the tank as a whole. But I would like to have that option per output.
Say I have a water tank with 2 output valves. Valve 1 goes down the line to production. Valve 2 goes to dump into the sea. Valve 1 set open, always sends water to production. Valve 2 set for just under full tank, and goes to dump the water instead of backing up up stream production when the tank is full.