This is how I setup my system.

http://biodiesel.infopop.cc/eve/ubb.x?a=tpc&s=447609751&f=444600361&m=813100992

I have no problems with air in the lines. And yes this way diesel gets into the WVO and WVO gets into the disel when I switch over. Once every couple of months I drive my main tank empty and refill it 1/2 way with diesel.

__________________
'84 300CD Turbo 132k (Anthracite Grey) - WVO - My daily driver - Recently named coo-coo-coupe by my daughter.
'84 300D Turbo 240k (Anthracite Grey) - Garage Queen
'83 300D Turbo 220k (Orient Red) - WVO - Wifes daily driver

I'm not a certified mechanic, but I did stay at a HolidayInn Express last night.