"NOTHING!"
There have been some bad explosions at incinerators. You don’t know what people are going to send you. Solvents are a problem. Do a search on “incinerator explosions killed”
When I was a young lad, we had an incinerator in our basement. I spent a lot of time playing with it. My best one was when I found some glass ampules of alcohol left behind in our attic by the people who owned the house before us. I put those in the incinerator. Blew open the cast iron lid, blew the metal stack out of the chimney, and put out an awesome fireball. Great BOOM, too! Didn’t set the house on fire.
My parents yelled down, “What was that?” My usual response to such questions was, “Nothin.” That was good enough for them.
"NOTHING!"