I've seen the caution about pre-filling a fuel filter. The idea behind the caution is that you shouldn't pour raw fuel into the large center hold of the filter as that is the output side of the filter assy.
I've seen mechanics use a plug in that center hole and then pour fuel into the outer holes...which then filters the fuel.
Some engines are picky about pumping dry...which is why, with precautions, it is best to pre-fill the filters.
2008 Fleetwood Bounder Diesel 38S, Flat tow-2015 Cherokee Trailhawk
Richard (KG5JAQ) & Margaret Kimball w/Shih-Tzu 'Charley'