My room that I am retiring from was not initially an art room. It was the only room in the school with a sink (we have 3 other art rooms), and that "sink" is one that you would find in a girls' bathroom, so it was not accomodating for 25 kids with their brushes.
Here's what I did, and found the system to work great. Mainly because the kids saw it as not having to clean their brushes, so I got ALL of my brushes back each day AND they were clean.
I put a large bucket UNDER the sink filled with water. I said "you don't have to clean out your brush just put it in the bucket". That appealed to their sensibilities I'm sure. Before you think I am not teaching them responsibility for cleaning their brush, I must say we went through the history and making of paint brushes, types and prices, and the proper way to clean them. I told them that our sink wouldn't accomodate 25 kids. They WERE responsible for their water containers, but not their mixing paletes (as there was another large bucket for those as well).
At the end of the day, I just dumped the water and cleaned the brushes and palettes myself, and in less than 20 minutes, viola everything was clean and ready to go. No aggravation on my part and I "saved" all of my brushes.