I bought it on taobao. The China version of Amazon/eBay. If you buy the caps with pressure relief valve simply unscrew the valve and mount a keg gas fitting. Just use it for carbonation.In your first photo the middle keg seems to have the standard cap on it but with a single post installed on it. I've never seen this before and checked kegland's website and it does not exist there. Is this something you drilled yourself? do you use it for fermenting or carbonating?