"Polishing" fuel at your level is accomplished by running the engine for an hour or so.
All diesels have either electrical or mechanical low pressure pumps that supply fuel to the high pressure rack.
They all pump more fuel to the rack than is actually used, there is a fuel return coming off the rack and going back to your tank (or the valves that switch for multiple tanks).
The pump on my W30 put out 25 gallons per hour - so essentially I was polishing 24 gallons per hour every hour of run time down to the 2 micron level (primary 20, secondary 12, on engine 2) as well as removing water.
Of course, that's not as good as a real polish, gunk accumulates on the bottom that the pick up tubes never get.
For that you take off the access and stick your hand in there and scrub, if you have a tank access plate. If not you make one