Originally Posted by Kegan
My black tank indicator was showing nearly full after emptying.
That is the norm. The only time the black tank gauge in any of my rigs showed empty was before they had been used. Those of us who have the inside the tank sensors really needn't ever bother to even look at that gauge because it is pretty useless.
Back in 2004 with my first van, I tried all of those tricks... geo method... ice cubes... and the next time the tank was filled and emptied, again it would still say filled. I even followed my father's RV toilet rule that anything that enters the tank must have passed through your mouth. Thus no TP ever. It still would never show empty. So... why bother? I have better things to do than spend half of the day trying to make a lousy gauge system work. I quickly learned to know when the tank was full, and if it mattered, I could always peek into the tank with a flashlight. Basically I just dump after every trip... or on long trips when I have the opportunity to do so. Empty... fill once with water... and empty again.
I always used Happy Camper and if you go to their website, they have good practical advice for care of a black tank. Though ours on a Class B are so small that one must keep that in mind. It is great for controlling smells in both the black and gray tank.