The OP decided to remove the Extend-a-Stay, but just in case some other members search on this, here's an edited picture pointing to the plug many others have been pointing out
The hose unscrews counterclockwise and this plug screws in (it's got normal threads, not some special counterclockwise thread gas thing).
I've been using the same thing for years except I leave my hose hooked up all the time. I have a female POL Cap
on the end that goes in the propane bottle. When I hook up the bottle, I turn off the main tank, unscrew the POL Cap and connect the hose to the bottle. Even with the leaky check valve in the hose very little propane escapes while I do this.