Unless your filter puked, there should be no appreciable grit downstream of it.
Flushing the system with fuel (carefully... If it were my choice I would use diesel or kerosene... much less chance of detonation and safe for the system... also a great solvent and lubricant) from a can and back into a recovery vessel of some sort by pulling the return line near the tank. Don't worry about stray diesel in the system as it won't hurt anything once you re-fill with gasoline... may even help! Use the current pump.
Removing the various components (working your way "downstream") and back-flushing or otherwise cleaning may also be necessary, especilly if grit does come out in the flushing process.
I agree that the pump sounds to be weak but don't put in a new one until the tank and system are free of KAKA.

Mike!