There are alot of different ways to go about this. And the way I did my wifes and will soon do my car is different than most.
My wifes '83 300D is running a 2 tank system on WVO. We live in FL and don't anticipate ever driving it where its cold enough to bother with coolant heating of the fuel tank.
My system consists of a heated Racor filter in the trunk right next to the 2nd tank. The fuel line runs under the car (zip tied to the existing fuel lines) to a 6 port switch. There is also a return fuel line running straight back to the tank. 1 input side of the 6-port valve is connected to the WVO lines and 1 input side is connected to the Diesel lines. The output on the 6-port goes into the lift pump and to the return line.
There is a little mixing of diesel and veggi in both tanks during the switchover from diesel to veggi. Ironically my exhaust smells better when burning diesel with a little veggi in it.
I'd recommend browsing around on the on the biodiesel discussion forums. SVO discussion.
http://biodiesel.infopop.cc/eve/ubb.x?a=frm&s=447609751&f=159605551
You'll find as many differing systems and opinions there about SVO/WVO as you will here when talking about motor oil
