I haven't done the freshwater yet and may not. I can just raise up the mattress and see it. I bought the 16" sensor, 6" sensor and it comes standard with 12" which I can use on the freshwater. Standard kit has 3 12's but you can substitute. You can see the side of the grey water tank while looking to the right of the black water tank. I will get some pics in the am.
I just used one wire from the existing black tank, brown I believe. Both tanks tie into one wire. In the wall I used the orange for 12 volts and white for ground. This took me a little time figuring out. I'm used to red and black. I still have use of the existing grey tank sensor for back up. The battery sensor give the reading in volts also.