easiest way to describe it is the big black metal thing sticking out on the firewall on the drivers side of the car and you pull off the rubber hose and the plastic elbow going into it then suck away

 

how would this affect injectors?

 

i'm not 100% sure on how this stuff works, all i know is that it works, i've had customers come in saying that they're getting 100-150km more on a tank of gas, i've also had customers come in saying when they were running 120 (75 mph) that they were running approx 400-800 rpm less

 

The only problem with putting injector cleaners in the vacuum side of the engine not all cylinders will get equally cleaned.

What it does when the engine is running, you are pouring the cleaner in the vac. hose. Which in turn will be sucked into the cylinders when the engine is running. The cleaner will do a couple of things.
1. It will clean the tips of the injector. Since its not going into the gas, it will not clean the insides of the injector.
2. It will also help in cleaning for the gunk on the intake valves as well.

I would be very careful on how much you put into the engine. Todays engines with all the sensors ect does not take much to screw them up.

Best way to clean injectors are with the proper equipment. Which most of the time you end up shutting off the fuel to the engine and just let it run on the cleaner.