
Your right On this one, It's so SIMPLE I'm Surprised anyone thought of it.
I agree if when you fill your Tank back up and there isn't any Unusual "SUDS" in the Water as you fill it up, You should have "NOTHING" to fear.
I also agree a little EXTRA Carbon in your Filter(s) won't hurt any either, it should HELP to remove any Trace elements of soap left over.
Now think of it this WAY, Whenever I put my hands in my tanks, somewhere along the line during the day I've Washed My Hands.
Now unless I've spent an Extra Long Amount of time just Before I put my hands in my tanks, in a Bath of Plain Water, Traces of Soap are going to be on them, Thus when I were to put my hands in My Tanks, I Would Still Contaminate my Tanks Water.
The Moral "UNLESS" You put your hands in the Tank Dripping With Soap or Suds, I take it You throughly Rinsed your hands before Drying them.
You Shouldn't Have Nothing to Fear.