I just cleaned a Yixing teapot and would like to show before and after pictures.
First a little background.
I bought this teapot in a lot at an antiques auction in Japan. It came as one of many 10s of items in a box on which I bid on the box. As such I didn't attach a price to it and only looked at it after having it for a while. I at first mis-identified it as a water dropper for calligraphy because of all the black hardened ink on it. It was only after I joined this board and actually had a different Yixing teapot come into my hands through the same route I went back and took a second look at this one. After trying to sell it a number of times online unsuccessfully and reading about Yixing teapots here I decided to take a scorched earth approach and try to clean it. It was after all "free" and unusable in its dirty state.
To clean it I put it into a pot with enough water to cover it and then some. I then put in about a 1/2 cup of table vinegar and a couple large table spoons of baking soda. I then lit the burner and brought the whole mess to a boil. After it was boiling I went back to my day job, ceramics, for about 20 minutes, leaving the concoction on low heat, bubbling away. After 20 minutes I came back and using a soft toothbrush I brushed away, holding the piece with chopsticks as it was hot. This I repeated 3 times. Here are the results. It doesn't have a residual taste either.