Just purchased a circulating heater that heats coolant from tapped hoses. I have installed one on another vehicle thinking that there was actually a pump moving the fluid, finding out now that it works like a perculator, just moving the hot water upward. This requires the tank and element to be lower than any part of the system and can have no air gaps. I dont know the direction of flow for the engine coolant through the system. The manufacturer wants you to pull out of a block drain and return into the heater core line that runs back to engine. I just dont know which one. The only drain I can possibly access is on the driver side, so the only way back to the heater core is over the engine which will create a "loop" which the manufacturer says cant happen. I am considering pulling from the drain plug on the radiator but am concerned whether or not this will create issues with the normal operation of the system. Any insight or suggestions in this matter would be greatly appreciated.