How to Clean injectors?

I'd visually inspect and clean them manually with some varosol and brake and parts cleaner first, then install them and run the high pressure injector cleaning system (the type like one of the ones 3M sells that's connected to the shchrader valve, not the "pour into your fuel tank junk you buy at the gas station) onto the fuel rail and let it go for 20-min or so.
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You should be able to rent one at any of your local parts stores.