The instructions are not clear about where you place the device. Do you place the entire device at the end of the longest run or do you place the device at the water heater and the check valve at the end of the Lawrence run meaning the faucet for this from the water heater? Also, the instructions indicate that the device should be placed on the cold water line. Is that correct? This is for a house without return lines using digital model 12PBG-18