I have made some progress figuring out the black tank configuration. I talked to Reace while at the Oregon Gathering in Bandon. He indicated the black tank sensors are on the curb side of the tank. The only reasonable way to access them is to cut a hole in the bathroom wall. He offered to send me a cover plate to plug the resulting hole. I'll try to avoid this.
Reace also indicated the tank is rectangular, but tilts up somewhat towards the front to better drain. Our 2011 has a 14 gallon black tank while the new 19's have a 19 gallon tank. I looked at a new 19' and it seems like the tank just extends further into the dinette seat area. Our black tank is 5 1/2" in depth.
I tracked down a manual for the existing tank monitor from KIB Enterprises
. I figured there would be 12 lines up to the readout (four from each tank). However, I pulled the readout today and found only 5 lines to the circuit board. I think they use two for +12v and ground. Then one line from each tank accounting for the other three. After seeing this I figured they are using a resistor network of some kind and decoding the resistance at the readout. From the manual I gather this is what is happening. The four leads from each tank come together in a small red bulb (resistor network?) with only two leads exiting the bulb. Further confirmation.
So, only three lines and a ground from the tanks to the readout. I could use two of the three for a SeeLevel system. However, my current thinking is to mount the SeeLevel readout on the side of the street side dinette. This would be easier to install and wouldn't disable the existing system. I'll likely mount a battery monitor, Trimetric, here also so it won't get lonely. Hopefully it'll be a few years till I can't make it to my knees to read them.
The black tank is 5 1/2" deep, the grey is 6 1/2" deep while the fresh water tank is 8" deep. The fresh water tank has a lip around the top so is not purely rectangular. This shouldn't change the reads much. SeeLevel sensors work on tanks 6"+ deep. They have a shorter sensor which could be used on the black tank. It might be advantageous to use the shorter sensor on the grey tank also.
All the tanks are readily accessible to mount external sensors on. I believe I can route the sensor wires through the hole for the battery leads (battery in the storage box). And 12v is easily accessible under the street side dinette seat. No reason to move the pump switch, so likely get a SeeLevel Model 709 which has no switches (other than to activate the display). I'll likely order one in the next few weeks.
The current monitor works OK, but I do want the added resolution of the SeeLevel. I am getting miss readings from the existing monitor. I suspect I need to refine the tank additives I use. Currently trying the GEO method with water softener and soap. But the grey and black read other than zero after emptying, just after and hours after. If anyone has suggestions on how much of these additives to put in I'd like to hear. Alternately, any other additive which plays better with the sensors.
Well, that's a long post. If you're still with me thanks. If you have ideas or suggestions please post.