Allowing it to flow down the drain of the sink or flushing it down the toilet is illegal in many areas, and finding a place to dispose of chemicals free of charge is not difficult.

In fact...

[link=http://portal.countyofventura.org/pls/portal/docs/PAGE/PUBLIC_WORKS/WASTEMANAGEMENT/DOCUMENTS/CLEAN%20UP-ENGLISH.PDF]Ventura area household waste pickup[/link]

Might be worth a look.