Here is a quote from the Keystone Owners Manual (April 1, 2013):
Sanitizing the Fresh Water System
Keeping the fresh water system clean and free of any potential contaminations should be a top priority. Sanitizing the system before initial use and thereafter annually, or whenever water remains unused for prolonged durations,
is recommended. This will help keep the water system fresh and discourage harmful bacterial or viral growth. Tosanitize your system, perform the following:
1. Drain the tank by opening the low point drains. Close the drains after water has drained.
2. Prepare a chlorine bleach solution of ¼ cup to one gallon of water for every 15 gallons of tank capacity.
Example: Use 2 ¾ gallons of the solution for a 40-gallon tank. If using Ultra bleach concentrations,reduce bleach to 1/8 cup to one gallon of water.
3. Add solution to tank and fill with water. Open each faucet/fixture until a distinct chlorine odor is smelled. Close faucets and let stand 4 hours.
4. Drain system and flush with fresh water until chlorine odor and smell is gone. (If a water filter has been added, change it at this time).
