Hi, I have never heard of a coffee colonic, but certainly the coffee retention enema. My understanding is that your aim is not to circulate the coffee through your colon, but rather to retain it in a lower position.
I have had lots and lots of colonics (I am 2 years along in a major colon cleansing program and currently on day 22 of the MC). My naturopath says most people do 3 in a series. I ended up doing considerably more than that due to extreme plaque problems (still passing garbage on day 22!!). colonics are a wonderful tool!
I cannot imagine coffee would be necessary after the intensive cleaning people describe with the flush, but I have used a coffee retention enema to relieve fasting crisis symptoms (toxic headache etc.). NEVER have I passed stones with coffee.
Look at the enema board this site for coffee enema info, lots there!