The second picture is the relief valve. Nothing should be connected to the relief valve.
To add an external tank, most folks purchase and install a tee between the outlet valve and regulator. Search the Internet with terms like "Extend-a-Stay," "Sturgi-Stay," "Stay-Longer" and the like. I installed this Camco 59123 kit. This link shows how to install it.
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Mark 2008 Holiday Rambler Admiral 30PDD (Ford F-53 chassis) 2009 Honda Fit Sport
Thanks for the info. I wanted to make sure of what that brass fitting was. I bought the Sturgi Stay fitting and hose but haven't installed it yet. The local guy that drops off propane tanks in this park took a quick look at my tank and said just get a $30.00 hose at the rv store and thats all I needed. I assumed he was talking about that bushing but I guess not.