I never know the answer to that either. I hate making a footprint making any painting: the canvas especially because of the space it takes up. I don't know about oils. I keep them so isolated I don't see how they are such a big deal like people think. In fact, I hurt the environment more with acrylic clean up because I can't really rinse them into my sink. I live on a septic. I am really careful to water them down in a glass or two, then I actually wait for it to disintegrate as much as possible before spilling the remainder into the sand outside! It's a very little bit and I bury it, but I feel terrible about it, even with that tiny bit. It's literally a few ounces.
With oils, it's all inside a Silicoil jar. I have been using the same one for two years now. I take them to the recycling center every year or two+ for disposal and the liquid that's inside the jar is far less than the water in the glass I spill into the sand regularly.
I give a thorough cleaning of my oil brushes about once a year, but haven't yet since I've lived here (almost two years). The Silicoil jar is filled with Turpenoid Natural and isn't like a regular turp. A small coat of that on the brush from rinsing them in the jar is fine to leave them flat for a long, long time.
As for the disposable palettes, it's equal as to what goes into the trash can (oil to acrylic).
That's my two cents on it.