Alternative chain cleaner/degreaser

With respect to mineral spirits, which is what I’ve used to clean new chains, yes - you can reuse it. Generally you want to let the spirits sit for a long while (months), and then filter it as you mentioned. This allows all the particulate to settle to the bottom where it’ll stay as you pour the good stuff through a coffee filter. Then you’ve got relatively fresh, clean spirits which you can reuse. Good thing too, because that stuff is pretty toxic.