An interesting page which explains the relationship with Yin and Yang. These Yin and Yang come from ancient Chinese traditions just as the roots of the Japanese tea ceremony do.
Sample from http://www.asianartmall.com/
” In the tea ceremony, water represents yin. The fire in the hearth represents yang. A stoneware jar called the mizusashi holds fresh water and symbolizes purity and only the host touches it. The green tea called matcha is kept in a small ceramic container called a chaire that is covered in a fine silk pouch (shifuku) and is set in front of the mizusashi.
If tea is served during the day a gong sounds, or if it is evening a bell tolls five to seven times to summon the guests back to the teahouse. Everyone purifies their hands and mouths once again, and then re-enters the teahouse to admire the flowers, kettle and hearth before seating themselves.
The host enters carrying the tea bowl (chawan) that holds the tea whisk (chasen), the tea cloth (chakin) and the tea scoop (chashaku). The tea bowl represents the moon (yin) and is placed next to the water jar, which represents the sun (yang). “
