For the last couple of years I have been going to my son's house after work and cooking a simple dinner for him. If he finished eating before I had cleaned up the kitchen, I would put his dirty dishes into the dishwasher. If he was still eating, or if he didn't feel like eating right away, when I arrive the next day, his dishes are still on the table.
It may seem to some that I have been very slow to address this, but I think you all understand that some things just aren't important in the grand scheme.
But my son has been well enough and stable enough for long enough that I have started asking him to put his dishes into the dishwasher when he is done. No confrontation, no big deal if he forgets, but I think it might become a habit if I stick with it. Such a small thing, but in our lives, significant!
And, I am fortunate that he doesn't bring food anywhere in his house other than the kitchen and dining room!
He also has developed the habit of putting his dirty clothes into a laundry basket in his room.