Opening a CO2 tank to clean it would void the hydro test. Plus CO2 is chemically pure, so there isn't any reason to bother.
In your kegerator unless you have a back-flow from a keg, you don't need to do anything with the gas lines or connectors.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk