I have been having some leak problems with my black tank and trying to get the red sensor to actually work. When you say you are using wood to shim the black tank are you just shoving it in between the tank and mold or is there certain points you have found best? Im trying to boondock more and although the black tank didn't show full it obviously was as it backed up very little into the bathroom sink (Joy). Im trying to figure out how to stop this in the future so I am trying to read upon. I will try and search for your post of your fix is you made one. Thanks for any advice you can send.