Pulling the fuel pump relay is the easiest way to disable the pump.

How are you going to pour the 'cleaner' into the system at a constant 40psi and have the engine running? Some of the 'cleaner' will be forced through the pressure regulator and back to the gas tank.

With most of the gasoline brands, cleaners are already present, making the injectors reasonably clean even after 200K miles. The only time I ever had problems with injectors was with a 25 year old car that was a driveway queen for 4 years (not started). I pulled the injectors and had them professionally cleaned after determining that one of the injectors was leaking and another was not spraying correctly.
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My back feels better when I sit in a Volvo seat