Lake Casitas Recreation Area is a campground that isn't too far out of the way if returning to Ventura or Santa Barbara. A $10 day pass will allow you to use the dump station there.

There’s a pay dump station in Fillmore, nothing else closer. We dumped on our way home at the Camping World in Santa Clarita; if you’re headed to I-5 there are free dumps at the rest areas at Frazier Park.