I have two clean up methods for brushes and palettes that worked for me over the years. The first one is quite simple. I got plastic buckets and filled them up with water. I placed one at each corner of the room (too disperse the crowd more than anything). The kid dropped their brushes in the buckets that were marked brushes and dropped their palettes in the buckets marked palettes. Then at the end of the the class I cleaned up all of the brushes and palettes that had presoaked. It took less than 10 minutes, and I would then stack the brushes and palettes out for the next crew. Of course I taught high school and didn't have the same classes back to back, and I also had the sink in my room. That said, my sink was so small it could only accomodate 2 kids at a time anyway so I had to devise a method to get everything done quickly.
My second method was to have a chart that had various tasks on it, and the kids were rotated through the clean up tasks and got a grade for cleaning (participation grade for want of a different term that you could justify). So there would be two kids assigned for brushes, two for pallettes, two for tables, two for putting work in the drying rack, two for making sure nothing was on the floor, two to take out the garbage, etc, etc, and these tasks were rotated weekly. This method became cumbersome for me, as I am not by nature someone who assigns clean up, I would prefer that kids take responsibility on their own, and found this, while it worked, another task for ME to do, and quite frankly it was a lot quicker and easier for me to just clean up the brushes and palettes. However, that said, if you can keep up with the list idea it is very successful, and kids stop complaining immediately when they understand it is rotated.
Just to add to the discussion on cleaning, my end of the year clean up went very well for 35 years. What I would do is take all the jobs imagineable in the art room including organizing closets, stacking paper, collecting pencils, etc, and put each on a small slip of paper (think fortune cookie). Then as students would walk into the classroom the last day of regular class, they would find me at the door on a chair with a hat filled with these slips of paper. They would pull their "task" out of the hat, and would spend the whole class period doing that task. They loved the 'luck of the draw' aspect, and by the end of the day with all 5 classes, my room was as clean as a whistle, and organized to boot. Again their was a grade involved, because they had to hand the little slip of paper back with their signature on the back of it indicating they did their task. This grade ultimately boosted their exam grade, and so they were eager to have the extra points.