L. - I came up with this story when my middle daughter was about 2 1/2 - she also suffered with constipation.
I asked her if she liked going to parties? She said Yes.
I asked her how she would feel if she wasn't allowed to go to a really big party? She said sad.
I asked her what she thought was at the other end of the toilet? She didn't know.
I told her that there was a big party JUST for Poopie People. They have fun and games and all their favorite foods and they are waiting for their new friends to arrive.
But guess what? She wasn't letting them go because she was holding on to them! That's not fair is it? No she said. SO I asked her to sit on the toilet and see if she could let a new Poopie go to the party. When she finally did one, she was all excited and called me to see. So we both waved good bye to him as she flushed him down. She actually said "Bye Poopies have fun" and closed the lid on him.
Voila! it worked. To this day she doesn't remember that story so it was never an issue later on. Long term memory doesn't fully develop until about 3 years old.
Some children think they are loosing a part of their bodies, and that feels wrong to them. What ever the reason, it was a stressful time for me before the story.
Try it - you can personalize it how ever you want. Make Pooping fun. Tell them not to touch a Poopie as it hurts their skin and stops them from swiming.
Regards
M. F