I agree with 94-Newmar, if it is over a week, drain it, including hot water heater. Make sure that the electric is shut off to the water heater, or you will burn up the heating element.
I sanitize every spring as part of the annual maintenance. Do a search for sanitizing the fresh water tank for the proper procedures.
03 Silverado cclb 3500 drw, D/A, Reese 22k hitch
07 Alfa SeeYa Gold 30RL,2 slides,power everything