I decant my brush cleaner too...but at some point it just becomes exhausted.
Marta, if you use lead, cadmium, etc. will the government's new toxic dump site take your sludge laden, flammable paper towels?
Sometimes, I think that the proper disposal of toxic materials is more important than the use. Way back when I was a signpainter, we only used heavily leaded paints. I paid the owner of a local gas station to add my spent thinners into his toxic material for disposal.
Many of my colleagues did not bother to do this...they dumped the stuff down the nearest drain or poured it out in the backyard. Alas, burning these materials does not rid the environment of the heavy metals either.
Sadly, I suspect that many "fine artists" are probably clueless about what to do with used turps. and toxic (and flammable) old paint rags. It is easier to just not use toxic materials.