The only real difference to speak of between my system and yours is the way you have situated your looped return, and your lack of sightglasses (MB primary fuel filters)
on the "T" fitting, my looped return is on the odd leg of the tee. That shouldn't make a big difference, but I switched mine to look like yours and it does seem more difficult to get the air out.
The way I made it work is this.
start your engine on diesel and switch to purge mode
open the hood and go around to the front. I notice you may night have enough tubing for this, so you may need to use a longer piece... KINK your fuel line between the TEE and the pex. this forces air to go to your veggie fuel filter instead of the fuel tank.
I don't always do this but it is helpful after changing the filter, and probably when installing a new system... I have the fuel filter with the screw on the bottom. after kinking the line back to the tank, I flip the filter upside down, unscrew that little cap on the underside, and let the purge mode push all of the air out of the bottom of the filter (it's upside down-remember) You will know when all the air is out of it because instead of hissing you will get a squirt of diesel (hopefully not in the eyes) at that time, unkink the fuel line that goes back to your tank, run back and open your tank to listen for air bubbles. if there are no air bubbles, or when the bubbles stop, go switch to WVO.
I personally would recommend swapping your looped return with your vo filter line... that SHOULDN't make a difference, but it seemed harder to get the air out your way.. maybe it's just me
