I bought a reducer and some 1/4" ID hose to connect to the liquid post (you can use standard beer line hose). Also you'll need some clamps for the hose.
You need something like this, you can find your exact size online: https://smile.amazon.com/dp/B07PMQQPT8/ref=cm_sw_r_cp_apa_glt_fabc_CSV62N95BK1RPHV2H576
Mine had no pressure as it was too old. Legally, I believe you're required to have someone depressurize it first.
A barrel is just a piece of metal with barbs on each end. A tee just has 3 barbs instead of 2. (I grabbed the first pic off amazon) https://www.amazon.com/Beduan-Fitting-Compression-Connector-Reducer/dp/B07PMQQPT8