If you are talking about the red clay flower pots like you get at Lowe's or something like that, then all you have to do is make sure they are clean. A bleach soak wouldnt hurt, but make sure you soak it in clean water for a while as the pottery DOES absorb liquids.
My son made caves and hideouts for his cichlids and sinos and it looks great and the fish use them all the time.
Why do I love fish? Because every time I stare into the little world I have created for them, every problem I have just floats away....