We actually camped at Kaibab Lake and then went to one of the two KOA campgrounds in Williams to dump tanks, get fresh water, get our battery charged up, do laundry and get ready for travel again. There are several options though for places to dump.

We dumped at Love's in Williams.

There is a Love’s next that we passed on our way through Flagstaff back home to the valley. There is also a Camping World/Gander up there with a dump station.

Hi! I believe the closest dump station would be in Williams at one of their campgrounds. I also know that a few miles to the east on I40 there is a KOA with a dump station for a small fee

There are dump stations in the town of Williams 3 miles away. You might want to check with the RV resorts there, or with the gas stations.