The connection you can see in the photograph is from a socket tool kit. It comprises a socket that fits the bolt that fits the end of the mill (I think it's 8mm), a universal joint (so that the drill can be a bit offset), an extension that fits the universal joint and an SDS chuck.
View attachment 17798
I used a framework of wood to raise the Mill to the height of the drill. (I wish that I had made the frame so that the mill sits higher up so that I could mill more grain without having to empty the FV. However, there has to be a compromise and if the mill is too high then it would be impossible to fit the lid on when it isn't in use.)
Whenever the mill isn't in use I put the lid on tight,
ALWAYS put a small unscented dehumidifier in the FV to stop any mould forming and
ALWAYS close up the hole with two lengths of duct-tape in an "X" shape to keep out any insects.