<< The mechanics typically use a much more concentrated FI cleaner than you can buy in the stores. The best way to keep 'em clean is to add FI cleaner evertime you get an oil change. >>
You want to know what they do? Unhook the fuel lines, get some tubing, attach one end to the injectors and drop the other end into the bottle. Then, crank on the engine for a bit and the injectors will suck up the cleaner. The FI will drink 100% concentrated cleaner.
That is exactly how I clean the valves on my motorcycle. I unhook the intake vacuum lines on each carb and split off tubing to each. I usually allow the bike's engine to run for 10min~ or so with the highly concentrated cleaner. It smokes so bad for that time period, it looks like I've gone and blown a seal; going through 1 bottle of cleaner in 10min is pretty concentrated. For the next week after that, I've seen some pretty nasty junk come out of the exhausts.