Never flush down the drain!
According to local regulations (Indirekteinleiterverordnung des Landes Berlin) waste water must not content more than 0,3 mg/l.
Dispose in a separate bottle.
The purpose of the following treatment is to reduce the quantity of the waste material and to save money.
Copper can be precipitated from aqueous solutions with hydroxide. Avoid an excess of the hydroxide since the copper will then dissolve again. Check with sulfide, if the precipitation is complete (black copper sulfide is formed). The precipitation may not work if there are organic compounds with hydroxigroups present which will give copper complexes (For example think of the tartrate used in Fehling solution). In these cases precipitate as sulfide in acidic solution. The precipitation is separated by filtering.