I also have dual Racor filters. You can buy them factory made complete with the valve and a vacuum guage or you could make your own with ball valves and fittings. I have two supply lines and two returns so with the use of a couple of valves I can direct the return from one tank to the other while running which sort of polishes it I guess, although I rarely do this unless I'm trying to shift weight (I generally go through fuel fast enough so I don't have to worry about stuff growing. I know it's a sailboat but we end up doing quite a bit of motoring around here). I had a filter plug up once when I stupidly started the engine while sailing heeled over in rough conditions and it turned into a major PITA.
Here's a (really bad) pic of our setup
Here's a link to the Racor setup:
MARINE TURBINE SERIES (2008) - Parker