Hi Eric, You are correct, the toxicity comes from what we throw down the drain, commingling our waste, including commercial waste: the paint thinners and bleach and factory waste and dead goldfish, as if the drain were a black hole where all bad things go straight to hell. But they don't. It would be good if we could reserve our sewers for biological waste. Even then, an astounding percentage of pharmaceuticals, pesticides, and stimulants pollute our waterways, toxic to wildlife, present only because we have first ingested them. Frightening what we willingly or unwittingly take in, only to make our waste unusable.