After reading all the replies it is now obvious that I made a mistake in trying to avoid adding too much water to my black tank. I think that on my first stop at a CG with a dump station I will stay hooked up, dump my tank, then fill the tank with fresh water then take it for a short ride then dump the tank again.
I was so afraid to fill up the black with water I wound up creating a problem
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EDIT
In the past when I was never more than 2 or 3 days between dumps I never worried about adding too much water, it seems that my concern about filling the black tank with too much water is what caused the problem
