Lynnmor wrote:
It is the slime on the tank walls between the "nails" that creates the electrical path causing high readings. Any slime, crud or corrosion on the nails can only cause a lower reading.
I concur, it's the slime. What can be used to strip that slime. I was thinking one of those LARGE bottles of something like Cascade dishwashing soap.
I will have to dig up my bore scope and take a look at the inside of the gray tank. Luckily my commode is on top of the black tank so I can tell from the sound of the liquids falling down the hole. A visual to verify.