An interesting observation from Wetpixel user David Haas:
"Since spring loaded buttons are the norm now on most digicam housings, Ikelite has implemented a feature to keep these buttons functioning over the course of a housing's lifetime. When I received my new Ikelite EOS 300D housing I noticed an extra little "flushing hole" alongside each spring loaded control. This larger diameter hole doesn't go as deep as the actual control hole, but allows you to pump more fresh water down into the tight area these little controls inhabit during a post-salt water dive rinse. A seemingly simple idea, I think shows they're constantly refining features on their products."