It does seem to me that using a simple fleet enema a few times probably wouldn't be sufficient for some serious anal play and ATM. I suspect for that there is need for a deeper cleaning. Back about a year ago Gore Gore Girl, a regular poster here, linked to a fascinating look enemas for anal sex. How to Clean Your Ass.
The abridged version would be that for a fast clean only add water to the to the colon and avoid the sigmoid. For a deep clean, get 'er up past the sigmoid and clean out EVERYTHING. I have no insight into this because I've never heard or read a pornstar say anything about it, but it seems to me that some anal scenes like with Mike Adriano or Legal Porno the ladies may go for a deep clean. 10" or 12" enema nozzles are available at Amazon.
I did read a while back (maybe in Ashley Blue's book? - a great read BTW) that some girls would use Imodium to simply bind themselves up for a while. This seems to be a pretty risky choice and it also seems like it wouldn't do anything to make ATM safer.
More recently there was a bit of an issue with Adria Rae not being able to complete an anal scene because she was weakened. She said, I recall, that (at least part of) her cleaning regimen was going without food. This also doesn't sound healthy. I'm assuming that girls who fast before anal probably also use some form of an enema.
Finally, I do recall one instance where a model said she did a deep clean the night before, ate light and then did a quick clean-out with a store-bought enema the morning of the shoot.
I wish I had some reference for you but I never expected to be weighing in on the topic...
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