I highly recommend the Horst Miracle probes. We just had them installed in our latest TT. Not only are they way more accurate, the capacity of the tank seems to be waaaay bigger. On our first trip out with them this year, after 4 nights (two adults), we were just hitting 2/3 on the black tank. Previously, the panel would have said we were full in 2-3 days.
This is our 2nd TT with these probes. Their performance is amazing. The OEM button sensors oughta be banned... :M
If you are installing new ones and don't have holes in the tank, I would look closely at the elevations that you install the sensors at so they more accurately read 1/3, 2/3 and full. Often, the sensors aren't close to being at the elevation they should be and you don't get an accurate reading even if the sensors and tank are 100% clean to start with. You now have a chance to improve upon what the factory would have originally done. I'm not sure if this has been discussed on this forum but I know there is a lot of great info. on the Forest River forum. If you go there, look for posts by Herk7769 as in this thread:
sensor mounting height
