A typical sensor is on the right ...the tip of the screw protrudes a very short distance into the inside of the tank, and a wire is attached to the head of the screw to show a reading to the monitor system inside the RV. There are normally four sensor probes per tank ... a ground probe plus one at 1/3, one at 2/3, and one at full levels. The erratic readings happen because the walls of both the gray and black water tanks become coated with slime and crud, and "stuff" snags on the protruding screw sensors. This causes conductivity between the sensors even when there is little or no liquid in the tank, and you have erroneous sensor readings. The end result is that you cannot trust what your sensor panel tells you ...you don't know how full or empty your waste water tanks actually are. While experience will teach you about how long you can go between dumps, it would be nice to have a monitor system that would give you somewhat accurate reminders!
the complete tank monitoring systems, wiring and all. Most reports from people who have tried one "cure" or another, even spending hundreds of dollars to replace the entire system, indicate there is nothing really works. We did read about one system of external tank monitors that did have some good reviews, but that is one that requires replacement of inside monitor panels and wiring along with the tank sensors at a cost of several hundred dollars PLUS labor. Then I read about Horst Miracle Probes. Based on their design (black tank right, gray tank left) and several reviews I have read, the Horst probes hold great promise for more accurate readings. The probe protrudes much further into the tank, and all except the tip is enclosed in teflon, which is non-conductive and self-cleaning. In addition, the black tank probe has a teflon "roof" over the actual probe to prevent paper, etc from catching on the probe and causing erroneous readings. The Horst probes use the original wiring and monitor panels, and the price is quite reasonable -- apx $70 for a set of both gray and black tank probes. So we decided they are worth a try.
The first task is to find out where the black and gray tanks are, and then to find out where the OEM sensor probes are installed on each tank. On our 2003 Winnebago Ultimate Advantage motorhome, the gray tank probes are behind a metal panel above the water pump in a basement storage compartment on the passenger side of the motorhome, pictured on the left. I found them about a year earlier when we replaced the water heater, which is located immediately behind the water pump compartment. The black tank probes are located behind a somewhat more difficult to remove metal panel in the water service compartment on the driver's side. I found them a couple of years earlier when I replaced the gray tank dump valve, located behind a lower metal panel in the same area.
Horst Miracle probe into the same hole, then attach the original wiring to each probe. Some RVs have molded in probes. In that case, you would simply drill a new 3/8" hole apx 1" or more to the side of the original probe, install the new Horst Miracle probe, and change the wiring from the old probes to the new probes. I encountered a possible problem with my gray tank when I found that the gray tank walls are apx 3/8" thick rather than the standard 1/4" thickness. The extra thickness of the gray tank walls made the well-nut type mount on new the Horst probes want to pop back out of the hole when I tightened them down. After some mental processing, I used a Dremel tool and small grinding wheel to cut a countersink area for the rubber head of the probes apx 1/8" into the tank wall. That left 1/4" thickness for the well nut to lock into, and worked very well! The picture to the right shows the countersunk Horst probe.
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