Saturday mornings are cleaning rooms and chore day (also known as hell). (I am ADD as well.) And if my ADD child hasn't taken his meds on Saturday cleaning becomes a HUGE ordeal. My husband was yelling and screaming at them. I told him to leave and I would take care of it.
I then had them get everything off their desk and put it into one pile. Then put each thing into one of three groups. Playroom, desk (or whatever) and "I don't know". Of course, 90% of the crap went in the playroom pile. We put the other two piles away, piece by piece. Then we seperated the playroom pile into the different categories; pretend, men, cars, etc. Then we carried each pile and put it away.
The main difficulties are: teaching the difference between trash, treasure, toys. Cause when you are 9 & 6, EVERYTHING is a treasure or a toy.
I realize that this sounds amazing that I, being ADD, could do this but I couldn't have done this a year ago or without my meds. And we teach most what we need to learn.
Congrats on a job well done! Your Saturday morning tasks/story remind me of a situation with my son. He had clothing PACKED into his dresser (I used to go in his dresser drawers and reorganize, but do no more; he's not a little kid anymore) and many clean clothing lying on his bedroom floor (nowhere to put them!!!). I asked him to make a pile of "give away" clothing, a pile of "keepers," and a pile of clothing to be moved to storage that "might" be worn again. Most of the clothing ended up in the give away pile. Normally, I would have protested, but a lot of the clothing are now too small (he had a HUGE growth spurt this past year or so). Anyway, it's satisfying to see organized drawers, if only for a short time. Actually, I really think he prefers when his stuff is organized, too. 
I don't have a specific day. We do it as needed.
I don't try to separate toys from trash. If my son values some colored piece of cardboard, he keeps it with his toys, and when he stops playing with it, I toss it.
I tell him that he has 30 minutes to clean his things up, and anything left on the floor goes in the garbage.
we do small chunks at a time so my daughter doesn't get totally bored--so, I will say 'empty 1 drawer in your desk put into donate, trash, and keep piles, and then come on down to take a break'. It takes a while, BUT she seems to do a better job if she has a short, reachable goal...we used to just say 'go clean your room' and she'd be down there for hours and get nothing done but to take everything out and leave it on the floor, so she could go from item to item to play with it!