You can dump at the KOA in West Yellowstone or Bozeman Town Dump. Also Madison Campground just inside Yellowstone (the west entrance) has a free dump.

Probably West Yellowstone at RV park.. or Bozeman Town Pump. I am not sure if cg is open now with flooding.

Don't know where you are travelling from, but as I recall, there are no dump facilities between West Yellowstone and Bozeman. We had been camped at Bakers Hole in West Yellowstone and we dumped at one of the RV parks in town (for a fee) before we headed up toward Bozeman. Several options in both West Yellowstone and Bozeman.

We headed south after, so dumped in West Yellowstone