Half the systems we blow out, we blow through the #4 testcock and on some weve cut in and put a riser with a cap after the backflow. As far as the backflow after we winterize the sprinklers we shut off #2 isolation valve on the backflow open all the testcock's and puff air in short bursts through the #1 test **** to prevent freezing. Not saying its correct, just the way im told to do it.
