Easiest and Safest way to refill 1 pound propane bottle

Here is how you can safely refill the small propane bottle and how to fully fill the bottle. Not just halfway or freeze your bottle. Straight up fully filled. Note: When I say air it means propane vapor. The purging of the bottle release the pressure so the liquid can enter easily. U have to open the valve to release the pressure so that green bottle dont get over pressure. That is the key to the safe refill.