even with the car on a slope i couldnt get the air out of the heater core completely, still got the waterfall noise. i found a better way to do it. get some a pair of vice grips and clamp off the line going to the heater control valve on the top. remove the heater core line comming from the bottom of the valve and quickly sumberge it in a bottle about half full of water or coolant mix, water should be fine. make sure the end of the hose is completely under water. Now, while holding the bottle, grab the upper radiator hose and squeeze it as hard as you can as fast as you can, its ok if water splashes out of the bottle, then hold it like that, wait for all the bubbles to go to the top. SLOWLY let go of the upper radiator hose and do it again and again until no more air puffs out when you squeeze. Now what i do is remove the radiator cap and remove the vise grip and reattatche the hose as quickly as possible, all those 3 things as fast as you can, i remove teh cap and release the vice grip in effort to let coolant flow through the heater valve and get the air out, then the displaced coolant can be filled into the radiator. THis worked perfect for me and no more waterfall/trickling water noise in the morning
