I have that exact model and its also a 2012.
Ours has 2 grey tanks that are both 23 gallons for a total of 46. (they do not equalize so our bathroom grey will be full while our kitchen tank is virtually empty...kind of annoying)
We have 1 single black tank which holds 31 gallons and find it humorous that our 19' hideout had a bigger black tank then this 1...anyhow...
My black tank almost always reads full or 2/3 full. Now our problem is that we are now on a seasonal site and the trailer is rarely moved anymore so its easy to see how that happens. However if you are moving it every time you camp then it shouldn't be an issue. Our 19' was always bang on but we would drive and then dump every time we used it and would then flush it out after draining. Never once had an issue with the sensors even after years.
You should be able to gauge how long you can go after a few trips without the use of the sensors....I have learned that our small family of 3 can go a bare minimum of 6 days before needing it dumped. (that's still using 5 gallons a day)
Now most people I know do not flush every time they use it or fill it up with water. For instance a lot of times if just peeing we will not flush and let that fill the bowl some....now if someone has to take a number 2 then there's usually enough pee in the bowl that no water or little gets used which in turn fills the tank far more slowly. Now if we filled the bowl half way with water and flushed every single time we used it then I could easily see only a couple days use.
Obviously I'm not sure how you use yours but I'm guessing its getting filled and flushed more often then it should.
Hope that helps.
2012 White Hawk 31DSLB
2013 F150 FX4, 6.2L, 3.73ELD w/ Max Tow Pkg