Hi Skroony. I heard the way to test your snorkel for leaks is to put a plastic bag over the head of your snorkel and seal it with gaffer tape or something. Then start your engine, if there are no leaks the engine should stall, if there are leaks it'll cough and splutter for a while depending upon the severity of the leaks. You may even hear it sucking air.

Hope that helps. regards
Len