Remove the black "QCC" fitting, it should be 1/4 npt..might need to heat it due to most asian suppliers use locktite..Get a 1/2 npt female to 1/4 npt male and you're done..if the 1/2 in line is regulated to low pressure, you'll need to remove the regulators connecting to the "Y"...
You have a tank adapter in your hand... designed for " tank pressure"