I'm quite sure it's just a slit, like on most macs. You just slide the disk in, and when you inject it, half of it slides out. Would work amazingly well, make taking out the disk much easier.
Yup some rigs simply deserve one, and this is up there.
PS. I am in incredibly early stage talks with david about organising some kind of competition in the future, though we'll probably start with something smaller than this kind of thing
If that happens, then my current project will have a point to it.
A PC submerged in an acrylic case filled to the top with UV Cooler Fluid. Watercooled, but the fluid in the tubing will be UV Black, while the Fluid in which the PC will be submerged in is UV Red.