Black holding tank won't drain past 2/3

[Ritkei]

After 4 days of camping we have a full holding tank. I open the black valve and hear a rush of fluids for about 1 min, then nothing. Check the tank level inside and it shows 2/3 full. After searching I found a post that suggested filling all grey tanks and pull all the valves at same time, causing enough of a vacuum to get the holding tank to drain. This worked once and now I'm stuck at 2/3 full again. Never seems to drain below 2/3 full. Any ideas or tips tricks?

[x96mnn]

DE88ROX wrote:

Roundtwo-40 wrote:
It should be noted that most black tank flush (external) hose attachments require the black tank valve to be OPEN during the flushing period. Just an FYI 🙂

Im curious as to why that is. I have a sticker on the side of my TT that says that.

I must admit though, that I do close it for a minute or two to let it fill up a little to help float away anything that's left behind that might not get rinsed. I know it probably does no good but.....

People have attached them, turned them on with the valve closed, walked away and forgot. This has caused a major mess inside and damaged some seals in the toilet.

[352]

Sometimes stuff gets stuck down there. Reach your arm down the hole as far as you can. When down to the max feel around for anything chunky. Grab it and squeeze it between your fingers until it gets smaller then dump some water in it (After you pull your arm out of coarse}. Do this once a month for regular maintenance. Wash your hands before cooking. I do have a self help video available. Hope this helps

[DE88ROX]

Roundtwo-40 wrote:
It should be noted that most black tank flush (external) hose attachments require the black tank valve to be OPEN during the flushing period. Just an FYI 🙂

Im curious as to why that is. I have a sticker on the side of my TT that says that.

I must admit though, that I do close it for a minute or two to let it fill up a little to help float away anything that's left behind that might not get rinsed. I know it probably does no good but.....

[DE88ROX]

I replaced my black tank sensors with these and my gray tank sensors with these

[DE88ROX]

Ritkei wrote:
After 4 days of camping we have a full holding tank. I open the black valve and hear a rush of fluids for about 1 min, then nothing. Check the tank level inside and it shows 2/3 full. After searching I found a post that suggested filling all grey tanks and pull all the valves at same time, causing enough of a vacuum to get the holding tank to drain. This worked once and now I'm stuck at 2/3 full again. Never seems to drain below 2/3 full. Any ideas or tips tricks?

Sounds to me like you have a bad sensor. I just replaced mine and noticed on one of the sensors I pulled from the black tank that it was all crusty. Most oem sensor are nothing more than a little button type stud that sits against the wall of your tanks. Any fluid running down the sidewall will come in contact with the sensor and send out a reading.

get yourself one of these its the only sure fire way to know when nothing more is coming out of your tanks. Plus, if you have a black tank rinse you will be able to know when its "clean" when you start to see clear water running out.

[wbwood]

Buy one of those clear view adapters so you can see what's coming out. Then with the black tank open, have someone flush the toilet inside continuously and see if the water is coming out. It maybe emptying all the way. Doesn't take long. I know our TT has a 32 gallon black rant I believe and it would be done within a minute when full.

[tenbear]

Have you been filling, at least over 2/3 full, the black tank before dumping? If its not full, fill it with water, then dump. This will help to clean the sensors, and if there are solids stuck in there it will help wash them out.

[gcloss]

I gave up on my black tank sensors. I simply push the flush pedal down and shine a flashlight into the tank. Simple visual check for black tank level.

[klm]

Once you are sure the tank has been emptied, clean the sensors if you must, back flush or fill and dump again - make sure you add some water to the black tank - you do not want the tank totally empty!! BTW, my sensors are useless, but my toilet sort of "burps" when flushed when it is about 3/4 full - lets me know it's about time 🙂

[rockhillmanor]

Fill with water dump. Fill with water dump.
That should take care of the pesky grundge that is now stuck on the sensor.

That usually happens when all you do is use the tank and dump without running a tank of water after each dump. No wand, special concoction added or whirrly gig needed....just a routine tank of water after each dump does the job.

When you are at a CG it takes all of 5 10 minutes to dump the tank and fill with water and dump again! I use my bathroom sink faucet to fill the black tank no fuss no muss.

I swear I must be the only one that the sensors work all the time. But I do believe it's because I run a tank of water after each dump! :B

[Markiemark32]

Discussed Here


Markiemark

[wa8yxm]

What you are seeing is normal operation of the sensors. the tank is empty, the sensors only work one time when new or one time after a power cleaning.

If you want the true level there are better sensors out there.

Horst Miracle probes are supposed to be better, I plan on installing later this summer.

SEE LEVEL works. and does not false, or so I am told, However it is expensive.

Of course any sensor system can fail due to a technical issue.

But the stock one, Slime on the walls, A piece of paper, anything that keeps the nail moist will false it.

[Roundtwo-40]

It should be noted that most black tank flush (external) hose attachments require the black tank valve to be OPEN during the flushing period. Just an FYI 🙂

[Dave_H_M]

Relax, that is the way they are spose to indicate after being used once.

Instead of all the magic stuff and whatever, I just let mine show what it pleases.

[trop-a-cal]

Time to but a spinning black water tank cleaner. They go into the toilet with a hose attached. They have a valve to start and stop the water flow. With the drain open allow it to spin until it loosens all the buildup. It's a stinky, messy job, as you need the exhaust fan on and have a bucket ready to put it into when done after shutting it off, as it will be dirty. An alternative is to put in a bag or two of Ice and drive the RV around to get the ice moving to dislodge the debre.