Make sure you test your underwater housing each day you are going to use it.
Do the O Ring preparation. Then take a few Kleenex, lightly bunch them up and put them in the housing. Immerse the housing in a sink full of water. You can easily do this on the ship. Leave it underwater for about a minute. Take it out, dry the outside off and then open the housing. If the Kleenex is dry you are good to go. If it's wet you have a problem and need to check your O ring for sand, etc. It's important to clean the housing and O ring with fresh water each night after you use it. It's all spelled out in the instructions.
Good luck. You will be taking some amazing pictures!
Renee - The better half of RobRen :-)
Carnival - Spirit: Alaska (August 8, 2007)
Carnival - Miracle: Exotic Western Caribbean (April 9, 2006)
Royal Caribbean - Explorer of the Seas: Eastern Caribbean (January 2005)