This adapter connects a 2L bottle with a 1/4" NPT adapter. The 0.53" hole is sized to be taped or a brass fitting can be screwed directly in. A 1"-8 UNC thread on the outside allows the adapter to be passed through a plate/bulkhead and secured with a nut, like the one from here http://www.thingiverse.com/thing:869643/#files.
v3 is usable as-printed. v4+ have a plug in the center that needs to be drilled out with a 0.5" drill. The plug is to improve bridging while printing.
*v6 increases the thickness of the plug; I had some issues bridging with the 0.4mm bridge in v4