Well, when I started my enemas/colonics back in the 70s after retuning from overseas duty, I would, at some of the facilities I went to, have my vitals taken, which included at times, depending where I went; a rectal temperature. I was told it was done for two reasons, first in that your core(rectal) temp was taken to assure you weren't running an abnormally high or low body temperature, and second, if you were within normal readings (98.6-100.2F Rectally)the second reading was taken to see what the water temperature should be that was going into your system and would be tolerable. And I was told rectal was the most accurate route of measurement and was also told, sort of on a lighter note, that if I were going to be given either an enema or colonic, what would be the, if any, issue of having a thermometer put in my rectum? I was advised it was more psychological and mental regarding peoples' experiences of having their temperature taken anally as opposed to the physical side of the procedure. Hope that helps answering your question.