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Old 05-13-2012, 04:09 PM   #1
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Black water showing full but not really full.

Now I have another question to post. This one embarrassing. LOL. The black water showing full. But not really full. Can see toilet tissue when flushing.
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Old 05-13-2012, 04:35 PM   #2
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Hi HuddJams,
Many RVs have sensors that can corrode or become contaminated with waste and/or waste paper. If the sensor has moisture on it, it will register on the monitor panel. There are several possible remedies. Some examples are:
1. Use a wand type pressure washer made especially for this task.
2. Fill the tank 1/2 full of water. Put 5 bags of ice cubes in the tank. Drive for 30 minutes or so. Stop and go driving is best.
3. As the tank is in normal use, add a chemical made to clean the tank an sensors.
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Old 05-13-2012, 04:56 PM   #3
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Nothing embarrassing in that question, everybody Poops.
Many have had success with the 'Geo method'

Here's a video with some tips too:


Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI
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Old 05-13-2012, 05:55 PM   #4
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You'll soon learn that when she burbs it is time to dump. Sensors are notoriously inaccurate. Water, and lots of it, best additive for tanks.

Barbara & David O'Keeffe
Figment II (Alpine 2002 36 MDDS)
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Old 05-14-2012, 08:17 AM   #5
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Black (And gray) showing full when the tanks are clearly EMPTY is what we call working as designed. I mean it is good they use those sensors on the black tanks cause they are.... black tank contents (IN fact, they truly are black tank contents being as they are inside the tank)

The GEO method where you empty the tank add 1/2 cup each Dawn Dishwashing liquid (Original blue, NOT antibacterial yellow) and calgon water softener, and then add water (I use about six gallons myself) sometimes works.

A good pressure wash wand such as the Valterra Master Blaster (Though I do not like that one, I like my home made one better, Same concept less chanse of the nose breaking off) sometimes works.

Horst Miricle Probes sometimes work

Chemical additives WILL NOT WORK (Save for cleaners cited above).

See-Level sensors WILL WORK, So why does the industry not use them?
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Old 05-14-2012, 08:58 AM   #6
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Like others said bad sensor readings are a common problem. We've used GEO method and back-flush with success over the past 2 years to keep the sensors working properly. Many RVers ends up installing better sensors like the SeeLevel mentioned above.

If you're interested I just wrote a post about tank sensor cleaning recently on the blog:
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Old 05-14-2012, 09:27 AM   #7
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My black tank started to do the same thing, so I purchased an adapter to screw into the bathroom sink, which came with a three foot hose from my local RV place. This then attaches to the sprayer wand.

You empty your black tank and then run only the hot water through the sprayer wand down into the tank from the toilet. Move that wand around, and if you can, gently get it down the "neck" of the tank toward where it dumps.

I leave the valve open, when I am doing this. Did a fantastic job and my sensors are now working as they should. My tank, when viewed from toilet, looks like it is brand new.


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Old 05-14-2012, 09:54 AM   #8
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The dreaded..........

If you see TP in the tank you may have the dreaded 'Pyramid of poo'. Often times that is accompanied with a blockage of the outflow.

In addition to the already good suggestions you've received here you may want to get a Black Tank Backflush adapter like this one :

Or you could make your own out of a non-valved backflush adapter and a seperate gate valve.

This is the best way I've found to clear a blockage.

I made my own cleaning wand out of a 4 foot piece of PVC pipe, a hose adapter with a valve, and a PVC cap with a SINGLE 1/4" hole spraying 90 degrees off the cap. It blasted the crap (pun intended) off the probes. Total cost of about $4.00.
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Old 05-14-2012, 01:59 PM   #9
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Like everyone said, these sensors are not the best in the world since they get clogged up real easy and then give false readings. Use lots of water to flush tanks each time you dump them. To get the sensors clean may take some work, but it can be done. Do like Muddypaws did and make you a sprayer or buy one from rv store. I spent a good amount of time cleaning my tanks with the sprayer and also used the ice method to help. Once I had them as clean as possible, I add about 1/2 to a cup of Dawn dishwashing liquid and a few ounces or liquid Ridex. I have been doing this way for a good long while and it works for me, plus the sensors work properly.
John- 2011 Fleetwood Southwind 32V
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