I was able to use a Mityvac to backflush my injectors with straight FI cleaner. Pull the injectors and strip off seals. Pour a little cleaner in a spray can cap. Set up your Mityvac with the brake bleed bottle attached. Wrestle the Mityvac hose onto the top fitting of the injector. Set injector upright in the cap of cleaner and pump up the vacuum. "Gently" press down on the injector to open the needle valve on the bottom and the cleaner will start to flush up through the injector, effectively backflushing it, including the screen.