Kama hitotsu areba chanoyu wa naru mono o kazu no dogu omotsu wa orokana.
Having one kettle you can make tea; it is foolish to possess many utensils. ~ from Rikyu's hundred poems
If you have only one kettle or kama, you had better take good care of it. Ordinarily you would fill the kama with cold water and put it over a charcoal fire to heat. For class we fill it with hot water to save time. Never touch the outside of the kama with your bare hands. The oils in your hands will leave permanent hand and finger prints on the cast iron.
First rinse the kettle with cold water. Then fill the kettle 1/3rd with cold water. Don't pour boiling water directly into the kama. Pour the water into a hishaku placed inside the mouth of the kama so that the water overflows and fills the kama. Ladle out hot water and rinse the outside of the kama until the kettle is one cup below the top of the mouth. Take one more scoop of hot water and put the lid on the kama and rinse the lid with the last scoop.
Lift the kama with the kan (rings) and set it on a towel to blot the bottom of the kama. You can now place it on the gotoku (trivet) in the tea room. The kan always travel together. Hold them properly side to side with the openings to the bottom. Put them in the lugs of the kama by holding them in front of you and taking one in each hand. Put the tail of each kan in the lugs and twist the left one towards you, the right away from you. Turn them only a quarter turn so that the openings will not come out of the lugs. Then rest the rings against the kama and pick them up from the top.
A kama full of hot water is heavy and dangerous so be careful carrying it so no hot water spills out of it. Carry it closer to your body to keep control of it. It is best to sit down first before attempting to put the kama down. Once the kama is situated and level on the gotoku take the kan out of the lugs by twisting them the opposite way you put them in. Open the lid slightly to let the steam out. Put the rings together to carry them back to the mizuya.
To empty the kama after class, put the kan into the lugs and lift the kama off the fire. Then stand and carry it to the mizuya. Place the kama on it's wood stand in the sink. Take off the lid and dry the underside. Ladle out hot water to rinse all around the outside. Reserve a scoop or two of hot water and then take two towels and turn the kama upside down, emptying all the hot water out. Use the hot water to rinse the bottom of the kama. If you have a kama brush use it to lightly brush the bottom in a circle and rinse one more time. Turn the kama over again (use towels) and gently blot the bottom inside. Be careful not to touch the sides as they are very hot. Put the kan in and pick up the empty kama, rest it on a towel to blot the bottom and return the kama to the gotoku to dry over the heat. Make sure that there is no more steam coming from the kama (if my glasses don't get fogged, it is dry) then turn off the heat and let the kama cool before putting it away.
If you care for your kama, it will last you a lifetime, and you will only need one.