One of the most frustrating things associated with RVing—and especially when boondocking—is knowing how much stuff is in your holding tanks. The longer you stay without hooking up to utilities, the more critical it is to know this information. When you are out of fresh water or your grey/black tank is full, you have to do something to change the situation, period. A full grey tank will back up and come out the lowest drain in the RV—almost always the shower drain. A full black tank will back up into the toilet. An empty fresh water tank is, well, empty!
The Bad News
Holding tank monitoring systems have a long history of being notoriously bad. This has been mostly based on the fact that nearly all the systems used sensors that were mounted inside or through the wall of the respective holding tanks.
Some sensors are designed with a screw placed in the tank with 12VDC power to it. One ground screw is usually placed at the first indicator level (usually at 1/3 Full). The downside is that the wall of the tank can easily become a conductor with a slight bit of scum or debris clinging to the wall and over the sensor screw. This creates a completed “circuit” between two or more sensors and will cause the monitor inside the coach to give you a false reading.
There is another system that uses head pressure of the liquid in the tank but that technology has proven to be very unreliable. The first problems usually occurred when debris inside the tanks would clog and sort of seal off the sensor. Even in a tank with a small amount of debris, the debris can slosh around and hit the sensor. When the RV is parked, this debris could possibly dry out to some degree and would render the sensor useless. The indicator light might be on or off and never change.
Both methods used the tank’s liquid contents to activate the sensor (inside the tank) and this would cause an indicator light to turn on. Typically, there was a small panel inside the RV containing these lights. The panels would usually consist of four lights—Empty, 1/3 Full, 2/3 Full, and Full.
For years, RVers have created homemade solutions to try to clean these sensors. These solutions are for the most part, myths, but among the efforts were dishwater detergent, water softener solution, and ice! All of these (and other goodies) may have worked for some RVers at some time but none of these have worked consistently.
The second real problem with the indicator lights (even if they are working correctly) is that they can only be accurate when the liquid is at the exact level of the sensor. Think about this…
Fresh Water Tank… Assume the tank is 100% full and on my coach, I have a 100-gallon tank. With a tank monitoring system using four indicator lights, the space in the tank between each sensor (and indicator light) is equivalent to 33 gallons of water. As I begin to use the fresh water, something strange happens to my lights.
As soon as I use just enough water to take the level below the “Full” sensor, the Full light goes off (because there is no pressure on the sensor). So the indicator shows 2/3 Full. But 2/3 Full is only 66 gallons of water—not the 95± gallons I really have on board.
As I continue to use water to take the level just below the “2/3 Full” sensor, the 2/3 Full light goes off and the indicator shows 1/3 Full. But 1/3 Full is only 33 gallons of water—not the approximately 66 gallons I really have on board.
But the most frustrating is that as soon as I use just enough water to take the level below the “1/3 Full” sensor, the 1/3 Full light goes off and the indicator shows Empty—not the approximately 33 gallons I really have on board! Is this nuts or what?
The Answer—SeeLevel Tank Monitoring Systems
A company in Granbury, Texas (close to Dallas/Fort Worth) first developed tank monitoring systems for giant oil tanks and used that same technology for monitoring RV holding tanks. Although the tanks on the RV are tiny in comparison, the monitoring system works the same.
First, there are no tank sensors inside any tank, period. Therefore, it is impossible for the sensor to become fouled from inside the tank. It is possible to fool the SeeLevel system. If the tank wall build-up approaches 1/2 inch thick or more with scum or debris, the system will pick up that mass as a water level—another reason to clean and flush your tanks regularly.
The sensors look like a long, narrow, green “PC board” that is flexible. They have two wires coming out of them that go to the monitor inside the RV. This “sensor strip” is fastened to the outside of the tank by means of an adhesive strip. You simply peel and stick the sensor to the tank. The sensor is about one inch shorter than the overall tank-height dimension so you center it vertically on the tank. It doesn’t make any difference if the tank is clear or black, the sensor works and is applied the same way.
Each strip contains tiny sensors over nearly its full length and therefore, will read a 3-gallon change in liquid in the tank. The individual sensors “read” the level of liquid in the tank by electronically measuring the density difference of the liquid or no-liquid, i.e., sensors above the liquid level read different densities than sensors below the level of the liquid. It is accurate and nearly foolproof.
There are no on/off lights in the control panel. The monitor displays a tank’s level in a percentage. You will know—approximately—how much liquid you have inside the respective tank. The volume calculation can only be determined correctly if the tank is a regular box-shape. Most holding tanks are not box-shaped due to design efforts made to enhance clean-out when draining the waste tanks. Therefore, the simple calculation of volume does not apply in most RV’s.
You will get used to your tank’s readings. My 100-gallon fresh water tank is box-shaped and a 50% reading is roughly equal to 50 gallons. But in my 56-gallon grey and black tanks, a 50% reading only means that liquid is half-way up in the respective tank. It does not indicate whether the top half of the tank is larger or smaller than the other half. Therefore, you will have to get used to your tank’s readings.
I Recommend It
I have recommended the SeeLevel tank monitoring system to many RVers and I’ve never heard a complaint. I’ve now used the system on two different RVs and will have it on any future RV I own. No, I don’t have any financial interest in this company. Their stuff works!
You can contact SeeLevel at the following…
Garnet Technologies Inc.
Suite 8, 125 M&M Ranch Road, Granbury, Texas, U.S.A, 76049
(Go here… www.rvgauge.com) Tell them Ron Jones told you to call.