Well, I wipe what I can from mine with a small spray of carb cleaner on a lint free rag. Then with the engine running I will take a spray bottle with distilled water in it and spray the turbo inlet. Probably not putting more than about 1-2 oz. of water through it in about 5-10 min.
I have never had anything but a slight gray film on the leading edges of the compressor blades. I cannot explain what it is, but I just do this process as part of my regular service and turbo inspection. The distilled water can do nothing but clean things up.