You have the flow right. Yes pull the thermostat. I feel for you John, scary when winters coming and you cant get the water out! You can also use the same idea and force some cheap RV anti freeze through it under pressure. I have a small 12 volt transfer pump I use to force RV antifreeze through Marine engines. Same idea as the air, just pump the anti freeze through it till it comes out. The direction wont matter. Upper hose to lower might be easier.