Best practices for disposing of waste that is diluted in water? (paint, finishes/membranes, cement, dust/particles from wet saw, etc)
Drying paint out is smart. 

Most cities have a hazardous household waste disposal service at the municipal landfill, likely as part of a strategy to encourage citizens not to simply pitch mineral spirits or motor oil or oil-soaked rags or consumer herbicides, pesticides, etc. 

Have you checked there?