In my studio, although I've been told this is not necessary, I decided to get a galvanized large trash can with a lid. I dispose of any material that has oils, solvents or cwm in this metal trash can. I did reach out to Gamblin Colors and they said really, the only concern of any spontaneous combustion is IF the materials get really heated in the trash can - and they said to just douse such oily, solvent filled materials with water and then you can put them in a regular trash can. However, I have gone the extra step of storing all such things in a metal trash can and I put the lid on at the end of the day!