Getting like an old record now but can't be stressed enough as one of our holidays was ruined by a flooded housing. A grain of sand or even a strand of hair is
all it takes.
We now even take an extra camera in case of flooding. Seems extreme but think of the cost and time
of that tropical holiday.
It takes seconds to rinse the housing in fresh water.
Regreasing the ring might take a minute.
Keep the housing door ajar with a cloth when flying to prevent the cabin's altering pressure jamming it.
Don't let your guard down. Everything works fine for ages then!
Check and grease the O-rings, grease. Do all that stuff. Always, keep an eye on that
After your first dive to a few metres, surface and check it. Every now and again recheck.