Normal method is to introduce city water (chorinated) into the tank several times and drain several times. This ought to be enough. Otherwise, use household bleach diluted mix to fill the tank once. Might help to drive around between after each filling to reach all the upper corners. Basically, tho, city water is all I have ever used to sanitize our tanks.
Normally, I don't drink the tank water, but use it for coffee and tea when boondocking. We camphosting at Island Acres east of G Junction. Be leaving day after Labor Day.
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