I never do this on the car as it's
extremely sensitive to the slightest bit of dirt.....
I dismount & clean the exterior of then pump then attach two short hoses and dunk them into a clean pan of fresh fuel (here in KHalifornia we no longer have Gasoline , we have " Motor Fuel " shyte) then connect it reverse polarity , it'll run and puke out some nasty crud....
Job all done , re-install with a new filter and it'll instantly gain several horsepower and start faster too .
FWIW ,. most every part of the (in)famous D-Jetronic FI system has tiny screens when the hoses connect and after a few years there's ALWAYS bits of crud and rust in these screens , taking the time to clean them yields significant rewards .