A new friend on CureZone suggests two chairs in the bathroom...a soft one for the shoulders, and a folding chair (covered with plastic) for the hips...plus the feet resting on the bathtub edge. They also said they didn't care for the 'bum in the air' position, which gives a graphic picture, doesn't it?
There are nice big see-through garbage bags that would fit well over a folding chair...the size I would use for cans or plastic bottles to the recycling depot.
Likely a folded towel or two would be useful...and/or fluffy washcloths, etc.
I was given an enema or two when I was a child...we had pinworms for a while.
I'll go back to the enema forum, or google 'how to enema' once more on the net...just to be certain I have the right/left side correct, and get the amount/retention time down pat.
Recently I read something about "gallons" with reference to enemas. I don't think so! Please, please, please don't use a gallon, my friends.
And please don't use it too warm, or cold. Easy does it, I'm sure.
It may be that no one has an explosive reaction to a mild enema...or that most can easily hold a small amout for, say, fifteen minutes, but a folded washcloth may give a person confidence.