Thor Forums

[blw2]

your rig is likely new I'm guessing
And since you are getting some sort of reading I'm going to guess that they are working for now.
and since you are asking this, I'm guessing you can't see down into the tank when looking down the throat of the toilet.... Like mine with a pipe shooting off at an angle from the toilet...
and if it's only 2/3 you likely have a good ways to go yet.
On my rig anyway I can get a lot of flushes in after it starts reading full.

On my rig, the flushes start to gurgle a bit as the level reaches the top of the tank/bottom of that pipe. this happens a good bit past full. it's pretty obvious. and from that point there's still a flush or two to go....

Oh, and be mindful that the lavatory sink likely drains into the black tank.

I felt a lot more confident about this whole endevour after I had filled the tank up once or twice flushing it out and testing things. What I did was this...sitting in my driveway, I filled the blank tank with fresh water. At first, while connected to "city water" from my house, I ran the water by holding the toilet valve to flush. That was taking forever...so I drug a hose in through the door....still took forever before it started getting towards the top.
My suggestion is to do this...either at the end of your trip since your tank is already nearly full, or in your driveway some day so you're not rushing at the park dump....and you'll get a much better feel for what's going on.