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Old 07-31-2014, 09:26 AM   #1
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Black Water Shows Full All The Time

Hello Everyone , I have a star craft 21 rb and the black water tank is showing full even know I have emptied it and flushed with fresh water. could one of the sensors or the ground to the sensors be bad? NEED HELP. p.s. it's a 2003 model.


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Old 07-31-2014, 09:35 AM   #2
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Most likely not a bad sensor, but you have something stuck on the top sensor. Might try filling the black tank with fresh water and letting it sit for a couple days. Then drain again and re-test. If that doesn't work some people put water and ice cubes in the tank, agitate by driving around a bit, then dump and test again.

Or do like most of us do and don't worry about the gauge or sensors and enjoy your camping. When it is full dump, otherwise ignore.

Hope this helps.

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Old 07-31-2014, 09:40 AM   #3
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Probably a piece of TP......
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Old 07-31-2014, 10:52 AM   #4
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Try adding Dawn detergent to the full tank of water. You could also use Calgon Water Softener, but it's hard to find. The additive will help make the water 'wetter' and dissolve solids that could be blocking the sensors. A drive down a curvy road will help slosh things around and help things break loose too.

Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI
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Old 07-31-2014, 11:05 AM   #5
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The standard sensor is a length of metal rod that sticks into the tank, the assumption is if the rod is wet, the level is at least that high, There is basically nothing that can go wrong with it.. HOWEVER....

if the wall the rod penetrates gets "Slimy" the slime can make the rod wet... And thus it sees the level that high.

how can I fix this?

Well, temp solution (works till the tank refills) is to blast the sensor wall, a tank wand called the Master Blaster by Valterra is one way to do this IF you can use it.. I kind of built my own even before I saw one for the first time.

(half inch PVC, cap the lower end, drill a quarter inch (or thereabouts) hole in the side of the cap in line with the indicator strip on the pipe. glue a garden hose adapter on top and put on a back flow preventer and quarter turn valve)

I actually used an elbow short piece and a cap on mine.

However with some toilets that can not be used.

Better solution:
Many have reported good results with Horst Miracle Probes. (google them)

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Old 07-31-2014, 04:27 PM   #6
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how much Dawn do I put in the tank?
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Old 07-31-2014, 04:43 PM   #7
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Originally Posted by taz1323 View Post
how much Dawn do I put in the tank?
About a cup should do for a full tank of water.

Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI
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Old 07-31-2014, 08:01 PM   #8
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Sometimes I will dip the used dishwashing water out of the kitchen sink and put it in the toilet. That usually keeps the black tank a little cleaner.
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Old 08-02-2014, 06:02 AM   #9
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Thanks to all Posters!!!

thanks to all that posted ideas. I am going to try the dish soap today along with the spray wand .I will let all know how it all goes

Thanks again, Taz.
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Old 09-21-2014, 06:46 PM   #10
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I have the same problem and bought a master blaster from EBAY. I hosed it real good last time we used it and haven't tried it since so I dont know how well it works. It sure blows the water out from the nozzle tho! A heads up keep your face back when you are spinning it around , DONT look or you will get a face full of spray. I keep telling myself it was clean water-clean water wife thought it was real funny until I chased her down to wipe my face on her shirt
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Old 09-24-2014, 03:50 AM   #11
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What i do when traveling i fill my tank at the quarter then put 2 bags of
ice in cubes than go the ice will hit the sides and take the toilet paper off the sensor good luck
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Old 09-24-2014, 05:19 AM   #12
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Many say this works good.....

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Old 09-24-2014, 07:18 AM   #13
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Old 09-24-2014, 07:24 AM   #14
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TAZ...get used to this phenomenon happening over and over again as you grow up RVing. If you use the RV regularly and flush the tank...you experience this on and off...if you drive and slosh the tanks frequently for the most part the tank level indicators stay free of debris.

Craig Gosselin
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