To get to the tanks, I'm just guessing as I'm not familiar with the sundance, is to remove the bottom cover. Then you will see the tanks and the sensors will be on the side.
I've done the GEO Method, which involves using laundry detergent and water softner. It will usually clean off a sensor that is totally out of wack, but by nature they are cheap OEM stuff and never reliable. Even on the more expensive methods they don't work.
I installed the Sealevel which is external and is not effected by waste materials. You can check out what I did on the link below.
//heartlandowners.org/showthread.php?t=7876