A bronze ding (鼎), a Chinese cauldron, from the late Shang dynasty (1556 to 1046 BC). Three-legged cauldrons like this, in metal or stone, are often found outside Asian temples. They're also found in witches' covens and in Greek mythology, where kings get cut up and boiled in cauldrons, in order to get reborn and youngified. 

In Daoism there are three body energies, known as the 'Three Treasures': Jing (your essence), Qi (the energy of the universe) and Shen (cosmic consciousness). To control and develop these energies, Daoism teaches you must first learn to fire up your inner cauldron, which sits in your lower belly (the lower Dantian: 下丹田). This can be ignited by learning to open and shut your anus like a bellows. Once you've mastered this technique you can learn to direct energies round your body and ultimately, perhaps, combine energies to transcend your body and attain immortality.