Dumping at Yellowstone

There are also dump stations at Canyon, Bridge Bay, Fishing Bridge and Grant Village. Canyon is even closer to Norris than Madison campground.

I have never been charged for using a dump station in Yellowstone, as far as I know they are all free.

Yes you can dump at Madison and there is no fee.

Mammoth has spigots spaced along about every other site. If you have a 50' hose and you are lucky you can probably fill your rig while parked in your site. When I was at Mammoth in 2011 there was spigot in our site. Last month there was one at the end of our site, but I needed a 50' hose and 25' hose to reach my fill point.