I have 2 - 24 inch pots and a 16 inch pot in my 180 gallon. All i did was soak them overnight in cold water.....they have been in there for about 9 months with no problems
I have clay pots in my tank and I just washed them first and put them in. I read in other forums that it might be a good idea to boil them first if they were used as planters since chemicals such as pesticide and fertilizers could have leached in them.