I've only had about a dozen colonics in my life. The first few were done with a therapist that had me undress completely, put on a gown that was open in the back, and then drape a towel over my legs. The second therapist that I used, let me take the colonics while I was totally undressed but always with a towel draped over covering my waist and my legs. I found the use of a towel mildly irritating, and sitting with my legs bent up at an angle on the table while trying to balance the position of the towel would cause cramping in my legs. When I first met the third therapist, the one that I currently use, I told her flat-out that I did not like wearing a shirt during the colonic because I am afraid that it will get wet or soiled. I also mentioned to her about the leg cramping issue with the towel and told her that I would prefer to go without one. She simply said, "Well, if it's alright with you then it's alright with me." So, all of my colonics with her have been with me completely nude on the table.
I have to say, my current therapist is my favorite one to-date. She is a much older lady, but totally professional and the focus is always on the colonic. I always undress completely in the bathroom adjacent to the treatment room (even including my socks), use the toilet there, and then walk back into the room naked and lay down on the table for my colonic. We always start with me on my left side, and do the insertion of the speculum and the beginning of the colonic like that. Then she has me roll over onto my back and the rest of the colonic is conducted like that. The first time that I took the colonic with her nude, I was a bit terrified of developing an erection and having her react very badly to it. When I do develop an erection (which I almost always do), it is ignored completely and the colonic simply continues. Sometimes she even asks me to spread my legs out flat along the length of the table, and then there is no possible way for me to hide my package or the erection---I just lay there completely exposed. I have caught her looking at my erection, and she even accidentally touched the tip of my penis once while massaging my abdomen, but again, it was totally ignored. I also chatted with her early on regarding my interest in enemas, which she just replied that they are a good thing.
Now, here is the best part: Her colonic machine broke very recently but I told her that I could come by with my enema bucket and do the treatment that way. Much to my amazement, she agreed. I arrived with my enema bucket, stripped nude in the bathroom and entered the treatment room. I sat on the edge of the table, a bit like at the doctors office as she kept asking me to feel if the water temperature was okay. Once I felt that it was, I laid down on my left side for the insertion of the tip and we started the enema flowing that way. She placed the enema bucket high up on a nearby shelf, and then she left it up to me regarding which position I would prefer to move into. I rolled onto my back and pulled my knees up to my chest with my legs spread slightly apart---no possible way to hide my erection now, but she says nothing. We finish with the first fill, I run off to the bathroom to evacuate, and re-enter the room empty but totally nude. She is busy with the second fill, and once the enema bucket is ready, we start again on my left side but I tell her that I want to move into the knee chest position. She has no problem at all with this, so there I am on my knees up on her table with my legs spread slightly apart and my chest and face down on the table. I can feel that I have a really solid erection, I'm sure that she has a full view of everything, and I can even see my pre-cum dripping onto the treatment table. She says nothing---just very professional and continues to administer the enema until I'm groaning out loud about how full I am. This all really happened, and I am going back to see her again soon.