Transfer switch on an AUX tank
 

Hey guys I have an 08 Duramax LMM powered Kodiak 4500, Im putting the saddle tank off a Freightliner in the bed so I can get better fuel prices. anyway, I want to put a electric diverter valve on the suction side of my aftemarket lift pump to alternatly suck the stock tanks or the tank in the bed. My main concern is I dont know if the LMM has a return line to the stock tank. I dont think it does I just dont want to be running off the bed tank only to be pumping fuel back into the stock tank, and over fill it.

So would I be able to use a 3 port valve or would the 6 port be necissary, with a return line to the bed tank?