I need to flash under water. Yep. Under water. There was a post on strobist about wake boarders who use PVC sealed with one end cap using a clear plexiglass piece for the flash to shoot through. I was thinking about doing something similar, but I want to have easy access to the flash/PW for battery changes if needed. Plus it has to be completely sealed so no water what so ever can get in. Pluss I'm going to weight it as it has to be able to sink. Is there any type of gasket or material that I can specifically use for a screw on piece that will reliably seal my contraption and can do so without having to be replaced after using it four or five times? Am I going to be using a ton of weight to sink a hollow sealed object that will probably have pretty good bouyancy?