/facepalm
Okay I will give it one last try then:
Barrel of Fluoride: Bad, don't pour it down the drain, it's harmful and you can get in trouble.
Barrel of Zinc Oxide: Bad, don't pour it down the drain, it's harmful and you can get in trouble.
Barrel of Phosphoric Acid: Bad, don't pour it down the drain, it's harmful and you can get in trouble.
Barrel of Formaldehyde: Bad, don't pour it down the drain, it's harmful and you can get in trouble.
Glass of tapwater: Fine, safe to pour it down the drain, it may contain a trace amounts of Fluoride but it's not going to harm the sewer.
Some white PC coolant: Fine, safe to pour it down the drain, it may contain a trace amounts of Zinc Oxide but it's not going to harm the sewer.
Glass of CocaCola: Fine, safe to pour it down the drain, it may contain a trace amounts of Phosphoric Acid but it's not going to harm the sewer.
Used Shampoo: Fine, safe to pour it down the drain (pretty hard to stop it in the shower also), it may contain a trace amounts of Formaldehyde but it's not going to harm the sewer.
And that my friend is the importance of context, instead of asking the sewer people you spoke to if something was good/bad you should have asked them if a trace amount of it used as an ingredient in a non-toxic liquid was bad (assuming you didn't ask that and get told the wrong answer).