Well, you're not going to like this:
I pull up a lawn chair, remove the seat bucket and use a toothbrush, rags and gojo hand cleaner when I clean my scooter.
Rinse with a moist rag, Dry & wiping as much as I can touch with rag or brush wrapped in rag.
When running it smells pretty good for a few hours afterwards!
I squirt some orange degreaser on the underside of the bike - work it around with a big soft brush and rinse with pump garden sprayer. Sometimes I use that expensive German made motorcycle cleaner/spray.
I don't know enough about scooter engines to flood things with water - but my goodness the Asians certainly have no fear of wetting things with car-wash like sprayers!
I like to keep things clean so I can more easily spot trouble if something leaks.
Stig