Lmfao. You sound like you've done this before.
Actually not nefarious, just some photo chemicals used in making DIY toners from constituent chemicals.
Since the mixed product is only stable in solution for a few hours.
So I ended up with a copper product. Sulfite salt, or something like that.
It gave the black and white print a red tint, that with hydrogen peroxideafter bathing or a few years of urban smog exposure morphs to greenish and white print.
But aqueous copper left when the bath exhausts turns kind of black with oxidize silver bits in it.
It is not healthy if put down the drain
I mean copper rich paint keeps ships bottoms from fouling.
Drying it, which means you can inhale dust residue, is not healthy.
So I had a 1l bottle of this waste stuff in the basement darkroom for a few years.
So in 2017 I was casting a concrete foundation in my back yard for a radio tower for a ham radio hobby.
Using a gas powered mixer using portland, sand, gravel and water to make the needed concrete.
6.5 foot deep hole 5 feet square. Lots of rebar too.
So mid mix one night where I was filling the middle of the form I mixed this waste in as a part of the water the concrete mix ratio needed.
Then the next load scour purged the concrete mixer and wheelbarrow clean.
So some day in the future if it is every really demolished, 4 feet down there is some copper bound to limestone gravel and sand in that part of the concrete.