On our Class C, I just flip the levers to the Sanitize Tank or Sanitize lines depending on which I want to sanitize. I have a small piece of hose that I attach to the city water inlet, put the other end in a bucket/gallon bottle of water and turn the water pump on. The onboard pump pulls the water out of the bucket/gallon bottle.
This is also how we fill the tank if we don't have a city water supply and need water. A couple times we ran out of water while on the road. We stopped at Walmart or wherever and bought a few gallons of water and pulled it into the fresh water tank. The water pump moves about 1.5 gallons a minute, so it moves through gallon bottles pretty quick.
-Michael
