Ok, I know some of those who hobby likes to perform TUHA and some providers like to perform TUMA. I personally don't do it because of the fact that it can cause Hepatatis, which I have learned back in 1989-1990 when I was going through USAF medical training as well as today being a nursing student. To me it doesn't matter how you think it's clean back there, but there's always a chance microscopic fecal residue are left behind, no pun intended, after a BM or flatus.
Let's say you are doing TUHA or TUMA on a chick (F) or chock (M), and then once you are done, you go for DATY and maybe LFK/DFK. How do you know that your tongue and/or lips/mouth did not pick up any microscopic fecal residue and transferred it to her vajayjay and/or lips/mouth and not cause you to contaminate her or each other? This is what we call in the medical field "Fecal-Oral Route" transmission. Just a thought and curiosity. Anyway here is a link for that topic:
http://hepatitis.about.com/od/preven.../fecaloral.htm