I have a 50 gallon SCA cube with all the stock plumbing. The tower has Durso drain approximately 1.5" and a return pipe approximately .5". I just upgraded my return pump to a bigger unit and am running an external .75" return up the back side. I want to turn the old Durso and return into a Herbie system to quiet my tank down but want to verify the larger of the two pipes (Durso side) should become the main drain and the old return should be the emergency overflow. I'm familiar with heights of tubes and how the Herbie drain system works. I just need to verify which one is which and if it will even work without re drilling for bigger bulkheads.