Both my kids had to use miralax as c was their main symptom. Mour gastro told us a double or triple dose for 3 days to get everything out, then follow the dosing on the bottle for adults. It's tasteless so justbmix it in with water. If the adult dose isn't enough use a dose and a half for awhile, you can't really overdose on miralax, it's plant based, if you take too much you just get the runs, then you know you need to take a little less.
But with probiotics you can create a healthy colon environment rather than taking laxatives which does not help you other than to go to the bathroom. I can't believe no one here takes probiotics!