I remember back when i had a torana, i used to rev the engine up a little and drop small amounts off water down the carbie and watch all the crap come out of the exhaust.
Done this every tune up i done and no problems. Realistically, very small amounts would form small droplets and go through the engine ok.
I think the method behind it is cold water hitting hot carbon would 'blast' the carbon off surfaces and spit it out the exhaust.