I've been playing Oxygen Not Included lately. Recently I mentioned I had this polluted water that seemingly wasn't getting dumped. Turns out this isn't a weird misprioritization. Instead, the algae terrarium building creates bottles of polluted water as a byproduct when it consumes CO2 and produces oxygen. I wasn't seeing the same bottles sitting in front of them every time; I was seeing bottles in the same places because the algae terraria kept replacing the old bottles.
So, one mystery solved.