Miller's Rest Area RV Dump Station (free) is located about 15 miles northwest of Tonopah on US-95. The rest area dump station is closed during the winter and might not be open yet. You can find location information and reviews for Miller's Rest Area RV Dump Station on Campendium.
Unfortunately, I don't know as we've never needed to dump there. I know a lot of RV parks wii let you dump for a few. There are apps that show where dump stations are.