Things I've tried so far:
1: Regular water: Easy and cheap. Not an enema. Just a seringe full. It might not give me the strong urge that laxatives do, but it does work 😃
2: Microlax mini enema: Of the laxatives, I've found this to be the most gentle one. It'll just give me an easy and smooth BM.
3: Dulcolax suppositories: These are little bombs. For me, they take about half an hour to 45 minutes to work, but when it starts, there's little I can do to hold it in. Explosive results. The downside I find is that it's quite irritative when I am pooping, so not very enjoyable for me.
4: Liquid glycerin: Instant results. It might not be very suitable for wanting to mess in a diaper a while after administering. When I squirt in 20 ml, it only takes literally minutes. If you're into mild scat (or bodily functions), it's a very fun way of making your charge poop during a change (like 'helping out a constipated baby or toddler') while saying sweet and kind encouraging words like what a big boy / girl he or she is. It's violent but in a good way. It does not burn like the glycerin suppositories do. What I also love, is that at times, it gives me the urge to push very hard.
5: Marshmallows: Messy and hard to insert. Results after 10 - 15 minutes. Quite enjoyable, and it does not burn.
I've not tried any oral laxatives yet, but I'm quite curious about them, especially because they last for a very long time.