Pre-Wetting Clay Pots and Charcoal to Sweeten Soil

It seems to me I remember my mother saying that a clay pot should be soaked overnight before using it? Also that charcoal makes the soil sweeter? If so where would I put the charcoal bits? in the bottom? on the top? mixed in with the soil? I hope you can help me. Thanks in advance.

I have not heard that clay pots need to be soaked before using. We have never done that and I can't say that we have seen any negative effects.
My mother was a huge advocate of using charcoal in containers, especially in containers that have poor drainage. She would put about 2-5 cm (1-2 inches) of charcoal on the bottom of the container, then fill with potting soil. She did not mix the charcoal and soil together.
I think the idea of putting charcoal at the bottom is to trap salts and other harmful compounds that will concentrate there as each watering leaches salts down the soil profile. Normally, when water drainage is good and the soil never stays waterlogged for too long, salts and other harmful compounds pass through the drainage holes out of harm's way.