Hey, I sank my Arctic Cat 500 twice. You started right by draining exhaust and air box but now comes the fun part.Pull the spark plug and spin it over to get the water out of cylinder and dry the plug. If you had water in the air box there is definately water in the oil, you will need to flush oil several times untill it comes out clean. I had to flush mine 11 times before it came out clean. (not milky). Also how clean of water did you sink in, I hope it wasnt muddy cause if you got sandy water in your motor you might as well go and trade it in. Run it a little inbetween oil changes to mix it up a little and once it comes out clean take it out and run it hard to heat it up and evaporate any left over moisture inside. Check oil as draining to see if you feel any gritty sand. If it was clean water you should be fine, GOOD LUCK!