This isn't exactly what you asked, as I am running straight veg on a second tank, but I do have an electric inline heater (in addition to coolant heating), and I have it wired to a toggle switch which is lighted as well. That gives ultimate flexibility for various fuel use. If I were to run blends, I either would not coolant heat the tank or lines at all, or I would have ball valves in the coolant lines so I could eliminate heating entirely when I wish to run diesel.

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Think Alternative Energy!
300CD '80 (now gone but not forgotten...)

Fractional crystallization is the concept behind what I am saying about clean oil plugging filters as the oil cools. This is the process used to separate air products, that was my exposure to it. Different components in the air freeze at different temperatures and pressures. A similar concept is fractional distillation which is one of the processes used to refine petro products.

Wire your heater with a fuse, switch, and relay.

That three port filter, I assume the vapor vent would go back to the fuel return?