Check with paint stores or hardware stores to see if they sell empty quart paint cans and lids. Acetone will break down dried epoxy some, and in a sealed can won't evaporate like it would in an open container.
I use ethyl alcohol (camp stove fuel) for thinning epoxy, and prefer it to rubbing alcohol as it has less water in it. I also only thin for using epoxy as a coating, such as on fly rod poppers. However, I have cleaned brushes with rubbing alcohol and as has been said it, it's best used with epoxy that has not cured.
I also use cheap plastic bristle hobby brushes for working with epoxy, and clean them for reuse, but eventually they get tossed. I used some natural hair brushes once, many years ago and learned they're not ideal if you want to try & salvage them.
