Having just cleaned out a basement of scenic supplies that have been building up for 18+ years, I actually ran into this same problem quite a bit.
My solution was to go to one of the Waste Management Companies around me, and they will get rid of anything for you, for a small fee per pound. (I just searched “drop off for hazardous waste, and my city.) Some places do an “Amnesty Day” where you can drop off anything for a short time, and they will accept it with no fee, but just last year my city did away with that lovely concept in favor of a new “you should make your own cleaners, and be sure to use all of your paint” education campaign. (Which is super unhelpful to people in our position). But even with the fee it was worth it. They took old Joint Compound, Jaxsan, stains, oil based paints, the works. And the fee was around 20$ per 10 lb (I believe) at my place, so if you only have one thing, it’s relatively cheap.
Hope this helps a bit!