What will you do if you need to stop on the way to use the restroom in the trailer? I would suggest about 15-20% fill to have on the road. And running city water thru the system as suggested above, will easily sanitize the piping/faucets.
2016 Tiffin 40 QBH
2015 38RSSA, traded
2005 TK3 #1869, 10 yrs of memories,
2017 F450 KR--one more Ford is it
2009 F450 4x4-died; 2010 F450-retired