Black tank says full but it’s empty

[rvshrinker]

Fairly new RV. Have rigorously followed instructions regarding emptying only when full, keeping water in the bottom, using a black tank tablet.

On a recent trip, I was surprised to see the black tank gauge read 2/3 full. I emptied it, a lot came out, then the grey, all good. But when I went back to check the gauges, black was still reading 2/3 full. Grey now empty. I filled the black with several gallons of water and a black tank tab. No change. Within the day, it was reading full.

Now I have not attempted the black tank flush, I assume through what ORV labels the “San-T Flush” because the instructions are poorly written and I want to make sure I get it right. For example it suggests I use a separate hose from my drinking hose, which makes sense, so I have to get one of those.

Please let me know how to trouble shoot this.

[ktmrfs]

Clay L wrote:

SoundGuy wrote:
Wildly inaccurate black & grey holding tank monitor readings are the RV industry's way of laughing at us all while keep a straight face. :W Until RV manufacturers completely ditch the use of in-tank monitor probes and upgrade to externally mounted sensors RV owners will continue to complain about this. Unfortunately, because manufacturers will always take the least costly approach this will never happen and as a result we'll all be complaining about this same issue years from now. My advice - ignore those tank monitors and simply use common sense to know when it's time to empty those tanks.

Since at least 2004 Winnebago has been using the TrueLevel external sensor system. Guess what? They are still inaccurate because crud builds up on the tank walls and fools the sensors. The Garnett SeeLevel is considered by many to be the best out there and when enough crud builds up on the tank walls it also quits indicating properly.

we have the garnet see level, have had it for 5 years, we camp 3 months/year. Yes, the warn that if you let crud build up it can affect the sensor. So far ours has been quite accurate. I flush the black tank at home, and use laundry detergent in the black and grey tanks to help keep any buildup off the walls. So far so good. However, I suspect if you let grease build up on the grey tank walls it will eventually affect even the seelevel, likewise with black tank buildup.

[Clay_L]

SoundGuy wrote:
Wildly inaccurate black & grey holding tank monitor readings are the RV industry's way of laughing at us all while keep a straight face. :W Until RV manufacturers completely ditch the use of in-tank monitor probes and upgrade to externally mounted sensors RV owners will continue to complain about this. Unfortunately, because manufacturers will always take the least costly approach this will never happen and as a result we'll all be complaining about this same issue years from now. My advice - ignore those tank monitors and simply use common sense to know when it's time to empty those tanks.

Since at least 2004 Winnebago has been using the TrueLevel external sensor system. Guess what? They are still inaccurate because crud builds up on the tank walls and fools the sensors. The Garnett SeeLevel is considered by many to be the best out there and when enough crud builds up on the tank walls it also quits indicating properly.

[Sillybugs2]

jplante4 wrote:
If you have a straight shot into the black tank from the toilet, shine a light down there and see if you're empty and just forget about the sensors. Worrying about such things while relaxing defeats the purpose of having an RV.

If you cannot verify that the tank is empty, then the Geo Method works as well or better than any magic pixie dust that Thetford produces.

Mark this day on your calendar folks. I agreed with SoundGuy 🙂

X2. We don't rely on our sensors much. If think getting full I turn off water and shine a light down to see how full. Hence why hubby had to empty at 7 pm last trip. My hirthday was the next day and I refused to walk to bathroom in the middle of the night somade him go. Lol that it started raining. He told me that dumping was my present. 🙂

[drsteve]

Soldier415 wrote:


Newbie question here, on my 5th wheel the instructions say to never run the black tank flush with the tank dump valve closed. Am I missing something?

The flush might overfill the black tank with water and overflow it inside your RV.

[Soldier415]

pryoclastic wrote:

rvshrinker wrote:
Please let me know how to trouble shoot this.

Not to worry at this point in time as it is a super common problem. Sensor(s) could have a something clogged up against it making it report a false positive.

I have tried several type of black tank cleaners and this is my favorite:

https://www.amazon.com/Kronen-KHT003-Handle-Holding-Treatment/dp/B00BFTZC3A

Pour some that down into the black tank and let it slosh around. When you pull into your next destination, dump black and see if that fixes the false positive.

If it does, use the holding treatment regularly and especially make sure some is in the black tank as you travel to slosh it.

Newbie question here, on my 5th wheel the instructions say to never run the black tank flush with the tank dump valve closed. Am I missing something?

[EnzoColorado]

I recently had the same issue. My black water tank is 33 gallons. I fixed it by pouring 25 gallons of water in the tank (5 x 5 gallon buckets) and tossed a enzyme packet in there and let it sit overnight. Then drove about 20 minutes to the nearest dump station, dumped the tank, then poured two more buckets of water through the toilet fast while the tank drain is open. This cleared up the sensor and also cleared whatever else is in the tank. Now I can shin a light down the toilet and see the plastic of the bottom of the tank, and no smell.

Link to the enzyme packet: https://www.amazon.com/gp/product/B00157TGXY/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1

[ktmrfs]

keeping the oem sensors working can be frustrating. Besides trying to keep them working, replacement Options include
1) horst miracle probes. they at least have a teflon insulator and a shroud on the black tank tip to keep TP etc off of it. just pull the factory sensors out, push in the miracle probes. They aren't foolproof but do work better than the junk oem probes. My experience, they are great on grey/fresh tanks, but can end up still being erratic on black tank.
2) sealevel or similar external sensor system: being external they are almost immune to bad readings. get enough buildup and they can be problematic, but pretty rare. Give a better reading of actual level, mine read in 5% increments but the systems aren't inexpensive. Sealevel works with std wiring, the other system I know of does not. Sealevel can't be calibrated to take into account non rectangular tank (e.g. black/grey) the other system can.

[hawkeye-08]

We have used the geo method for years (no bleach, just water softener and detergent). We switched to just using Dawn last year with 4-5 gallons of water. Have not had any sensor problems in the 10 years we have had travel trailers. Our current trailer had a poop pyramid that was stubborn to remove (purchased trailers used). I think some don't put enough water in after they dump. A few gallons is taken up by filling the drain line to the dump valve I expect, so if you only put a few gallons in, not much in tank, just filled drain line..

[jplante4]

Dennis12 wrote:
I've had the same issue. I think that this was $14 but worth every penny. I understand that Camco has newer one with a spinning head on it. Go with it from here on Amazon.

Don't get the one with the spinning head.The heads break off and eventually jam your dump valves.

[Dutch_12078]

SidecarFlip wrote:
Simple answer is... If you want a reliable monitor, get an external tank sensor. Not hard to install. 100% foolproof

X2... Our SeeLevel II external sensors never misread, and the percentage readouts on the monitor are much more accurate than the OEM "screw through the tank wall" sensors and monitor systems. Easy installation using the existing wiring.

[SidecarFlip]

Simple answer is... If you want a reliable monitor, get an external tank sensor. Not hard to install. 100% foolproof

[DutchmenSport]

blownstang01 wrote:
Fill the tanks roughly 1/4 full and add about 1/2 cup or so dishwasher soap (liquid) before you leave for next trip. When you get to the site, dump the tanks and most likely they will work. I've tried other methods and this by far works the best for me. The dishwasher soap is made to dissolve the grease and sludge that's grounding the sensors. I also do this every 5th or 6th trip as maintenance cleaning, have not had a sensor give a false reading in 5 years of doing it this way. Good Luck !

Agree 100 percent. Been doing this on 3 different travel trailers over the years and my black tanks sensors work quite well. I don't use that much water, just about 4 or 5 gallons, enough to really slosh the dishwashing liquid and/or bleach around real good. This is the best thing you can do.

Second best is to use a toilet wand, as pictured above. Shove it down the toilet, open the outside valves and spray away.

My current trailer has black tank flusher. I never close the outsdie valve when use it. I attach the hose, turn on the spigot, then open the camper valve. When everything gets dumped, the force of the spraying water will continue to push anything lingering behind, including hitting the sensors. But I found driving with clean soap water in the tanks does the best. I use Dawn, about 1/3 cup and about 4 - 5 gallons of water. Only rarely do I use bleach. Not necessary.

[blownstang01]

Fill the tanks roughly 1/4 full and add about 1/2 cup or so dishwasher soap (liquid) before you leave for next trip. When you get to the site, dump the tanks and most likely they will work. I've tried other methods and this by far works the best for me. The dishwasher soap is made to dissolve the grease and sludge that's grounding the sensors. I also do this every 5th or 6th trip as maintenance cleaning, have not had a sensor give a false reading in 5 years of doing it this way. Good Luck !

[Dennis12]

I've had the same issue. I think that this was $14 but worth every penny. I understand that Camco has newer one with a spinning head on it. Go with it from here on Amazon.