Well I have a son with Asperger's traits who is 9 and has real difficulty still with this. Poor boy also has constantly 'loose' stools -and we still don't know why. Consequently, he can't really manage yet alone, so I help him with those moist Kandoos. However, it's pretty urgent that he needs to learn to DIY, as he goes away on a school trip next yr. When he's (rarely) stayed with friends before, he's come home with poo on his sleeves, bum and pants, smelling.
So this is what I'm currently working on: I'm breaking down each part of the task into tiny steps and getting him only to do one step at a time. We first did - "roll up your sleeves ABOVE the elbows". Then we did, "Pull off about 5 squares of toilet roll and fold them so that they're a nice strong 'wodge' that none of your fingers will go through".
Then (and we're still on this bit), I do most of the wiping with Kandoos and he does the very last wipe with the ordinary paper "Make sure you've got right into the crack and rubbed either side of it". The reason for this, in his case, is to build his confidence (he's pretty phobic about the whole thing) and always end in success - a clean bum, with minimum effort.
My next step however will be "look at the paper and see if you can see smears on it? If so, repeat the same thing with more paper etc etc"
The problem is that he almost NEVER has a poo that is firm and formed, so it ALWAYS ends up smeared up his outside bum cheeks. He's slightly dyspraxic and so can't easily do what's needed to scoop and wipe it all off efficiently. But eventually, he's going to have to do the best he can, shower frequently and have lots of spare pants to change into. But he'll also need to be AWARE that he needs to check for smearing.
So in many ways, in this area, he's v much like a 3 to 4 yr old who's just learning - except with maximum embarassment now, poor thing.
The hardest bit will be how to help him wipe the first 4 to 5 times when there's a lot of runny poo, without getting a lot on his hands and I think I'll also have to do, "check your hands and if they're dirty, wipe them with toilet roll before continuing on your bum". There are actually a LOT of component parts to the whole task, including of course the handwashing afterwards. I'm also afraid of making him phobically paranoid about a bit of smearing or obsessive with handwashing - which can happen in children like him. So it's really difficult!
But generally, to parents of younger DCs, I'd say get them to get good enough at one part of the process and then move onto the next, if they're struggling - otherwise accept the extra laundry and ensure they bath regularly!
Blocking the loo with too much paper is of course another whole ball game!