"I would want it to function like the IP designers intended" doesnt hold up to scrutiny. If you did then u could ONLY use diesel .... You could not run any WVO and still stay in the parameters of what the IP designer’s intended using your rule.
They built their system with the parameters of design calling for diesel not WVO. I would bet good money that with WVO as a parameter then they would design them differently.
Also, "none of them do it" (return WVO fuel to tank instead of Looping.) That’s a misconception for sure. Maybe none of the "kits" but a whole lot folk return WVO to the WVO tank just for the reason you suggest. It's easier to deal with air. The ones who loop...... they do so to ease the stress on the injection pumps fuel lift. Also, I assume the "kit" manufacturer are covering their butts so they cant be sued for helping to create an IP failure in a customers car due to their kit putting to much stress on the IP pump.
Many folk do return to their veg tanks. Then there are others who loop just cause the kits do.. while others loop out of educated necessity cause they understand that with the type of IP's they have on their engine they know they need looping and/or an additional electric lift pump to reduce the stress on the IP from pumping more viscous fuel. This is an area (to loop or not to loop) I’m still unclear on from my studies. I would do a search on the subject to get more info.
As to "kits" I like Greasels 3in1 hose. I would do some kit bashing and use the Greasel 3in1 hose, and the system from
Neotric of Canada This is how I would do it, if I was doing it with a kit. I'm planning to design my own hair brained experimental design.
Best site IMHO for info and discussion is
Biofuels BB but I am partial to bulletin boards over Mail list..