Nikkei EXTREME X5 User Manual page 43

You can test by closing the case without inserting the camera.
Submerse the case completely in water for about a minute.
Remove the case from the water, dry off its exterior with a
towel, and then open the case. If the entire interior is dry, the
case is safe for use under water
After every use in salt water you will need to rinse the outside
of the housing with non-salt water and dry. Not doing this can
eventually cause corrosion of the hinge pin and salt buildup in
the seal, which can cause failure.
To clean the seal, rinse in fresh water and shake dry (drying
with a cloth may cause lint to compromise the seal). Re-install
the seal into the grooves in the backdoor of the housing.
Please note: the waterproof case is rated for use up to 45
metres deep.
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