I never played with soap suppositories, and a soapy finger only a few times, but...
Before we had access to the toy firetruck my playmate Janet and I often used fingers to stimulate each other resulting in a bowel movements.
I think she did me first time we played and said she did it to herself to make her "poo."
As I was always (and still am) up for anal stimulation, using a spit coated finger she penetrated my anus, and fairly quickly I felt things move and produced some good results.
Then it was her turn, again a spit covered finger, in as deep as I could go, and wiggling the tip. I wasn't long until I could actually feel the poo move into her rectum, and I was presented with good results. Then she wanted me to do it again, and we repeated several times until there was no poo left. I'll never forget that great feeling of the poo moving into her rectum.
She liked to be on the receiving end, so I would usually have to do her before she would do me. We did it with another of our playmates, Donna, a few times, but she was always scared we would get caught, and one time we did. It was by Donna's father, who took her into the house and sent us home. What surprised us, he never called our parents, but until we started the fire truck enemas, when curiosity overcame fear, Donna never participated in our poo play sessions.
Biggest surprise, playing with Janet and having the results come out like soft serve ice cream, and lots of it.we called it Janet's pudding, it only happened once, but both of us hoped it would happen again.
With my mom's enemas and analy oriented playmates, no wonder I turned out like I did!