I have slow bowel transit, and that results in hardening of the stool. By the time it reaches the rectum, too much water has been removed in the large bowel. The function of the large bowel is mainly to remove water before it reaches the rectum. As a result of the slow transit I have, I need to take a PEG 3350 solution to keep water in the stool so that it doesn't get too hard to pass.
The stool hardening problem doesn't happen to me, but I understand what you mean, as this did happen to my son. He used to have similar problems to TaniaAust's daughter (very severely slowed transit, constipation, frequent hospitalisations etc). He was prescribed something similar to this PEG stuff, and it did help. But he still had to take two other types of laxative as well and often have enemas.
I think this stool-hardening problem is why fibre makes things worse for many people. It used to make my son worse. If it doesn't have enough water to keep it soft it practically turns into rocks inside you! As I understand it, the PEG stuff works a bit like fibre (helping peristalsis work more effectively with something to push against) but it actively draws water into the gut and holds onto it so the stool cannot harden.
In the end my son got better when he was put on antibiotics and probiotics long term. It seems his Lyme disease, or maybe some other bacterial infection in the gut, was causing chronic and severe inflammation. His tummy works fine nearly all the time now.
But, back to me and my innards. I always used to have terrible diarrhoea (I mean up to 20 times a day). The doctor made me test myself with charcoal to find out intestinal transit time, and despite that degree of diarrhoea, I had a 48 hour transit. Fibre gives me actual formed bowel movements but doesn't speed up or slow down the traffic.
Since doing the same antibiotic and probiotic treatment as my son, I have much, much less pain and rarely get diarrhoea, but I do still have everything in slow motion.
So I think there has to be some other reason for it.
Sorry if I didn't explain this enough before, I was trying to avoid being too graphic in explaining things!