Done the twin tank setup on jcb fastracs at work one tank for red and one for white diesel,we fitted 2 time delay valves into the lines to allow red to return to its own tank during changeover so as not to contaminate white tank,the tricky part is calculating the time taken to purge the fuel system we worked it out on fuel filter volume,ie feed return line into measuring jug swap over tanks work out time to fill until you see the white running through,work out how much filters hold then calculate the time using the time taken to fill the jug then add a bit extra time to allow for fuel in the lines.
Hope you find this useful
Stewart