Holding tank level indicator 101

**Herk7769** · 03-07-2010, 07:56 PM

Could use some real help understanding how this system works. Various posts show conflicting information. I have a 2010 Flagstaff 8526RLWS.

1) HOW, exactly, does the system indicate water level?

2) Do the 3 switches penetrate the tank? or are they just glued to the outside and use capacitance to indicate level?

3) Are the reported voltages additive? I.E. if the TOP switch is fouled by debris stuck to the wall, does the level of the tank read "FULL" or 1/3 full? and similarly if the TOP two switches are fouled with dried stuff, does it always reads 2/3 Full until the BOTTOM switch is covered and then it reads FULL.

4) Once you are in this crappy situation, what is the best way to CLEAN the walls of the tank?

I have been dry camping for a month now and I believe my idea of how it works has merit. I am hosed (so to speak) since I have been dumping when the tank reads full, but not getting a full dump (since the tank has not been full). I am afraid to just let it fill until I see liquid in the trap.

Any help in my understanding or tips on getting out of my predicament. I will be in full hookups tomorrow, and plan on driving there with liquid detergent and calgon in the gray and black tanks. Then I plan to black water flush and see if that fixes it. What to do about the gray water (always indicates 1/3 full when empty) I have no idea. (I think there is dried soap on the top switch).

NWJeeper · 03-07-2010, 09:09 PM

Usually the indicators are not switches as most people think but rather two bolts placed in close proximity to each other at set levels that penetrate the sidewall of the tank. Current is then passed from one to the other once the fluid level covers them and completes the circuit. I am not sure if they complete the ground side or if they actually pass +12 volts through them but I would guess that it would be the former as it would only require one wire for each set level to be run to the tank from the meter, the other side could just be attached to a nearby ground.

If you do not have a built in tank cleaning setup then you can purchase wands at RV supply stores that have holes in all directions in the end. The wand is connected to a fresh water hose and you put the wand down the toilet opening and turn on the water to flush the tank. Cleaning the grey tank isn't as easy. For this reason it is important that you not let food particles get down your tank or for that matter grease. If I needed to clean the grey tank I would fill it about half full, add a degreaser or cleaner of which you can also find at an RV supply and drive the rig to slosh the water around then empty it.

Stock fluid level sensors in most RVs are notoriously bad and fall short of being really useful. There are solutions on the market which work much better. The Sealevel monitor system is one but there are others.

Dave_Monica · 03-07-2010, 10:48 PM

The See Level II tank monitor looks very interesting. Has anyone installed one of these? Do they remain accurate? Looks like they use the existing wiring.

Dave

cfsoistman · 03-08-2010, 07:14 AM

We saw the Horst Miracle Probes demonstrated at the Hershey RV Show. Little pricey but they fit in place of your existing probes. I just wish the probes on our tanks were accessible for replacement.

http://www.rvprobes.com/home.html

**Herk7769** · 03-08-2010, 07:55 AM

Thank you for your prompt replies. Since I have a belly cover, I will need to get home and drop it to examine the connectors. I will let you know what I decide to do.

NWJeeper · 03-08-2010, 02:35 PM

Quote:

Originally Posted by Dave_Monica

The See Level II tank monitor looks very interesting. Has anyone installed one of these? Do they remain accurate? Looks like they use the existing wiring.

Dave

I have been thinking about it Dave but other things have been in need of my money (like the converter/charger) so it is low on my list right now. Does look like a fairly easy install because you use the existing wiring. Means you can just jumper off of the display in the wall and add the Sea Level below it and not have to worry about runing new wiring into what for us amounts to be a very hard place to get wiring to.

**Herk7769** · 03-08-2010, 04:50 PM

So, why does the tank read 1/3 full when the top sensor is the one fouled?

NWJeeper · 03-08-2010, 05:10 PM

Quote:

Originally Posted by herk7769

So, why does the tank read 1/3 full when the top sensor is the one fouled?

How do you know that it is the top sensor that if fouled? I have never been able to actually see the sensors inside the tanks. If that is the case I couldn't tell you.

**Herk7769** · 03-09-2010, 07:43 AM

Good question! It is a real puzzle.

Here is the timeline.

Black tank:

Read empty Lowest light on.

At 2/3 full Only top light off, I dumped tank. Did not get a "Full Dump" in the blue boy. Maybe 15 gallons from a 30 gallon Black water tank. (I have a 42 gallon blue boy)
Lights did not change even though tank was now empty.
(2/3 full indicated)

After using the tank a few more days, tank indicated FULL (all lights on)
Dumped tank again and indicator went back to 2/3 full. Again, did not get a "Full Dump" in the blue boy. Maybe 20 gallons this time.

Got into full hookups and dumped tank and flushed for an hour or so with factory installed turbo flush till water clear and stayed that way. Let tank fill with clean water again and dumped all clear water.

Tank now reads 1/3 Full (bottom two lights on) when empty.

What do you think is going on?

MtnGuy · 03-09-2010, 08:27 AM

Quote:

Originally Posted by herk7769

Good question! It is a real puzzle.

Here is the timeline.

Black tank:

Read empty Lowest light on.

At 2/3 full Only top light off, I dumped tank. Did not get a "Full Dump" in the blue boy. Maybe 15 gallons from a 30 gallon Black water tank. (I have a 42 gallon blue boy)
Lights did not change even though tank was now empty.
(2/3 full indicated)

After using the tank a few more days, tank indicated FULL (all lights on)
Dumped tank again and indicator went back to 2/3 full. Again, did not get a "Full Dump" in the blue boy. Maybe 20 gallons this time.

Got into full hookups and dumped tank and flushed for an hour or so with factory installed turbo flush till water clear and stayed that way. Let tank fill with clean water again and dumped all clear water.

Tank now reads 1/3 Full (bottom two lights on) when empty.

What do you think is going on?

Definitely no expert on this, but here goes:

On a previous trailer that I had where I could see the probes, they were positioned at about 1/4, 1/2, and 3/4 levels. So when I had 1/3 tank showing, that meant that the fluid level was at 1/4, 2/3 showing meant the fluid level was at 1/2, and full was when the fluid touched the 3/4 probes. If you think about it, that makes sense, since these are approximations, and gives you a general level of your tanks. You certainly wouldn't want the full probe at the very top of the tank....that wouldn't give you any warning at all that you needed to watch out.

There is no probe for the empty position......that light always stays on.

Now my question to all of this, is if your actual bottom probe is at 1/4 of a tank, then are you sure that you are completely emptying the tank, or at least the fluid is below that probe ??? The reason I ask is because of my own situation. I could never seem to completely empty my black tank....there was always fluid in the bottom, and after charging a little water into it, the 1/3 light would come on. When possible, I would tilt the trailer to the street side, hoping to help empty the black tank. Last fall before winterizing, I pulled the bottom down to see what was going on, and lo and behold the pipe comes out of the middle back side of my tank. I drove my truck up on blocks and dumped, and the tank completely emptied. But......my gray tank pipe comes out of the curb side front of the tank, so to completely empty that tank I have to raise the street side and lower the tongue. And to further complicate my winter weatherization, I have to raise the curb side to completely empty my fresh water tank. Geez.......the neighbors think I am crazy.

My point is, if the tank is not completely emptying, then that might be why your 1/3 light is still on.

**Herk7769** · 03-09-2010, 10:49 AM

Might be a lot of truth here....

These are photos of my tanks during the manufacturing process.

http://travel.webshots.com/photo/254...X?vhost=travel

http://travel.webshots.com/photo/238...w?vhost=travel

It looks to me like the outlets are right at the bottom of the tanks so they should dump completely as long as the hitch pin is higher than the rear bumper.

The left tank (from the back) is the gray and the one on the right (with the white hose - black water flush line) is on the right. What confuses me is there is a probe at the very bottom on the left of the outlet and then 3 probes on the right of the oulet.

I assume the left probe is the ground and the 3 probes on the right are the lights. You can see that the lowest right probe is very low on the tank and the highest probe is also not at the very top (your observation seems right on!).

It should dump empty from my view even if the trailer is level. I will try another dump later today and use another heavy flush cycle.

NWJeeper · 03-09-2010, 01:08 PM

Quote:

Originally Posted by herk7769

What confuses me is there is a probe at the very bottom on the left of the outlet and then 3 probes on the right of the oulet.

I assume the left probe is the ground and the 3 probes on the right are the lights.

I think you have it right on this assessment. I would think the one contact on it's own is the ground. I've seen lots of different arrangements for tank monitors but I've never seen them be all too accurate. Ours started acting up this last summer but I drove some clean water around the block and it seemed to dislodge what ever was messing with our sensors.

**Herk7769** · 03-09-2010, 02:31 PM

OK, just turbo flushed with the rig at a steep angle with the drain openings facing down. After several minutes of flushing, I re-leveled the rig and lo and behold it read "empty."
My elation was short lived however, when I added two bowls full of water and 4 oz of holding tank liquid to the black tank and it immediately showed 3/4 when I checked.

The gray water still shows 1/3 even when totally empty.

bumma'

NWJeeper · 03-09-2010, 03:46 PM

Quote:

Originally Posted by herk7769

OK, just turbo flushed with the rig at a steep angle with the drain openings facing down. After several minutes of flushing, I re-leveled the rig and lo and behold it read "empty."
My elation was short lived however, when I added two bowls full of water and 4 oz of holding tank liquid to the black tank and it immediately showed 3/4 when I checked.

The gray water still shows 1/3 even when totally empty.

bumma'

Sounds like a Sea Level system in the future for ya. I think you need to get it and let us know how the install goes and how it works.

**Herk7769** · 03-09-2010, 04:02 PM

I have been looking at it for sure.

mjones12 · 03-09-2010, 05:09 PM

Quote:

Originally Posted by NWJeeper

Usually the indicators are not switches as most people think but rather two bolts placed in close proximity to each other at set levels that penetrate the sidewall of the tank. Current is then passed from one to the other once the fluid level covers them and completes the circuit. I am not sure if they complete the ground side or if they actually pass +12 volts through them but I would guess that it would be the former as it would only require one wire for each set level to be run to the tank from the meter, the other side could just be attached to a nearby ground.

If you do not have a built in tank cleaning setup then you can purchase wands at RV supply stores that have holes in all directions in the end. The wand is connected to a fresh water hose and you put the wand down the toilet opening and turn on the water to flush the tank. Cleaning the grey tank isn't as easy. For this reason it is important that you not let food particles get down your tank or for that matter grease. If I needed to clean the grey tank I would fill it about half full, add a degreaser or cleaner of which you can also find at an RV supply and drive the rig to slosh the water around then empty it.

Stock fluid level sensors in most RVs are notoriously bad and fall short of being really useful. There are solutions on the market which work much better. The Sealevel monitor system is one but there are others.

Jeeper: Thanks for your description of how the sensors work. I was afraid that the spinning wand (aka Stinky Slinky) might somehow damage the sensors, but with your description it seems that there is nothing to fear.

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