Bob, It is highly unlikely you would access the tanks from the bottom in your rv.
Post a picture of your water bay area and someone that has or seen your model can tell for sure.
I will attach a link to some pictures. They are not current and the modification have come a long way since taking them. However they may guide you to a solution to your problem. The wet bay had a plastic panel that was so large that access behind it was impossible. Eventually an aluminum panel was cut to replace it and make accessing behind much easier. The nice vinyl just refused to stay stuck to the panel and has been replaced by carbon fiber looking material that has worked much better. Behind the panel the gray and black tanks are stacked on top of the water tank. The sensors are on the sides of the tank and thus accessible. I suspect your two toilets are fed off the same sensors but if not they likely are mounted next to each other an hence your toilets get very similar readings. Carefully removing the middle sensor and reattaching it solved my too early indication.
Once the panel was out the water hose reel was reversed to make the hose drop straight out the bottom instead of through a hole where it liked to bind. The switch for the reel was replaced and it now powers in and out.
The macerator was mounted on the floor and rarely used as well as making service impossible so it was removed and stored in a newly found space on the opposite side of the wet bay. Pictures show how that was accomplished.
The sewer drain pipe did not center on the bottom which was not a problem for the macerators little hose however a normal stinky slinky was very hard to attach. The hole was enlarged and screw in deck plate solved that.
The water faucet was turned over for better use. The slide valves now have a small hole on their face with a stainless screw to cap it. A few sprays of silicon each year and they stay nice and smooth.
The electric toilets allow installing the commode in many more places by using a pump to push the waste through a pipe versus letting gravity do the job.