as far as i understand you already have an in tank walboro 255 fuel pump. that pump right now is pumping the fuel to your filter. therefore what i'm telling you is to simply add an inline walboro 255 fuel pump inbetween the one in your gas tank and the fuel filter. therefore you have 2 fuel pumps running in tandem.
wire in another 30 amp 12 volt relay and use the black/pink fuel pump relay signal wire (ground) to click over that extra relay for your extra pump. just tap into the existing black/pink wire.
1 and 3 = battery constant 12 volts
2 = the fuel pump relay signal from the ecu (just tap into the one already there for your intank pump)
5 = goes to the positive terminal on your inline fuel pump (put a 30amp inline fuse somewhere in between here for safety)
then ground the other terminal of your inline walboro.
done, gl
Dave