Are you sure that your Itasca didn't come with the upgraded sensors that sense liquid levels through the walls of the tank?
There's actually nothing "inside" the tank with these type sensors. Winnebago puts them on many of their models right from the factory. Our 2005 Itasca has them and they're been very good - especially if we keep the black tank clean with occasional rinses using the wand or by back-flushing. I believe that these through-the-tank-wall sensors are one of Winnebago's "features".
However, our Itasca toilet is mounted directly above one end of the black tank so that it's a straight shot down into the tank. We can check the level with a flashlight by looking down the toilet, if necessary.