Couple ways...

You could simply take the line where fuel exits from your fuel filter and tee it into the fuel supply line just before your heaters. This would be always looped. The draw back to that is that if you get some air trapped in the system it no longer has a way to get back to the tank and will have to be run threw the engine.

Another way is to take the line exiting the IP and the injector return line and tee them together before the filter. Send that to a valve(mechanic or solenoid) that gives you the choice to run looped return or full return. The valve could either send fuel back to the tank or to the filter then back to the fuel supply.

There is plenty of room to mount an aux pump at the tank output and that would be a great place to put it.

Settling will remove a lot of animal fat if temps are warm enough. Centrifuge really doesn't remove much fat because you have heated the the fat enough to turn it into liquid and it passes threw the centrifuge. Filtering at ambient temps will remove a lot of fat but you will go threw a lot of filters.

Installing a fuel temp and fuel pressure gauge are also a must for me when running any wvo. They can really tell you a lot.

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1982 240D 617turbo 4-speed 225k miles ,boost and pyro gauges, home made two tank SVO setup
1982 240D "Cream Puff"auto 313k miles two tank SVO setup
1996 F-250 Powerstroke 186k miles, bone stock (possible donor for the 1970 F-350)
1970 F-350 "Bertha" 460, 4-spd, 72k miles, 12 foot flatbed, needs a diesel!