Black holding tank won't drain past 2/3

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

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 :)

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.

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.

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.

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.

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

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.....

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 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.