After sanitizing as above, close the valves that enter and exit the water heater. Remove the drain plug and drain the heater. Put the drain plug back in. Remove the pressure relief valve and fill the heater with vinegar. Put the pressure relief valve back in. Run it through a few heat and cool down cycles, then pull the drain plug. Get a water heater flush stick and give it a good flushing. After flushing, open the inlet and outlet valves, fill with water, turn it on and enjoy the fresh smelling water.
The video says to ride around a bit to move the water around inside the pipes and tank. I don't feel there is any need to do that. Just fill the system, leave it in the water system for a while then dump it.
Generally speaking, you should drain your water heater after each camping trip if the water has been heated but then allowed to sit in the W.H. for an extended period.
Here is a bit more detailed explanation of the cause (from http://wellowner.org/water-quality/hydrogen-sulfide/)
"The magnesium rod used in water heaters for corrosion control can chemically reduce sulfates to hydrogen sulfide...
Hydrogen sulfide also can enter surface water through springs.Hydrogen sulfide is a colorless gas that can exist naturally in groundwater. Sulfur-reducing bacteria present in groundwater use sulfur as an energy source to chemically change sulfates to hydrogen sulfide. The bacteria use sulfur from decaying plants and other organic matter in oxygen-deficient environments. They can occur in deep or shallow wells, and reside in plumbing systems."