Black Tank Shows 1/3 Full After Drain, Suggestions?

[Joe1969]

After draining the black tank completely, nothing more coming from the septic hose, the light shows 1/3 full. Galley and Grey drained and show empty. All other gages working correct. Any idea what may be causing this?

[chuckster57]

Probably moisture. Try draining and leaving the valve open for 15 minutes. If it shows empty, then you may have TP stuck on the side.

[travelin texans]

Then again you may just have the typical sensors, useless after the 1st tank full.
In 45 years of rving I could count on one hand the number of folks that said "mine work just fine!". Yet I've never gotten a good answer as to how they've determined "they work just fine"?
Do they stick the tank like gas stations? Do they measure liquid in & out? One person said "because I know my tanks & how we use them!", that didn't convince me much that theirs "worked just fine".
Yes mine work just fine, I have 3 sets of pretty red lights that light up every time I push the button. But the bath reads 1/3 as the showers filling with water & just emptied the black, nothing more running out, yet the sensors show 2/3s, but the little red lights are lit.

[Canonman]

Here is a link to a company called Kleen Tank: https://askkleentank.com/how-do-my-r...-sensors-work/
In short, most sensors, particularly the black tank sensors have problems due to "stuff" getting on or clinging to the sensor itself. The best way to get these sensors working again is with a thorough flushing of the tank.
Try this: Fill you tank using the black tank rinse sprayer. When the tank is full pull the valve and dump the tank leaving the sprayer running. When the tank is basically empty close the valve and do it again, at least 3 more times unless the sensor starts working sooner.
In some tanks the sprayer head is installed such that it doesn't hit the sensors but many do. In any case filling the tank should loosen any "stuff" causing a sensor problem.

[Max23]

After dumping. Put 10% of your tanks capacity back in it with water. As you drive to your next spot or whatever, the water splooshes and splashes around and helps keep things cleaned off the sides. Might help, don't know how stuck on things get in there. Things can be awful clingy.

[Canonman]

Max brings up a good point. The owner of Kleen Tank suggests 3 gallons of water with a Calgon (Borax or Arm and Hammer detergent enhancers work as well) PineSol mix (we use a cup of Borax and a cup of El Cheapo detergent mixed with a couple gallons of water after each dump) then let it agitate as you drive down the road.
Here is the actual recipe from Kleen Tank:
Mix 40 ounces of PINE-SOL® with 8
ounces of Calgon Ageless Bath Pearls in a
gallon jug. Top off with enough water to
fill. Shake gently. Allow foam to die down.
Use four to eight ounces (as directed) in
each tank (more in especially hot
weather or if your tanks will be filling up
slowly over time).
We like our method because we can premix the dry detergents, store them in premeasured ziploc bags and just add water after we dump.

[dutchmensport]

Joe1969, the reason your black tank readout is showing a faulty reading is because "crud" is stuck to the sensors on the inside of the tank.

There are 3 wires attached to three different metal rivet type things on the inside of the tank. These little rivets are notorious for catching "crud" and the "crud" hangs on and does not fall off and drain away. So the "rivets" think they are still under water.

This is very common amoung RV users. Basically, those sensors are useless, especially in the black tank.

There are tricks to keeping those sensors cleaned and working, and yes... if you REALLY work with it, yours will always work too. But it does take a lot of effort.

The solution to keeping them working is to do something to remove the "crud" sticking to those "rivet" metal sensors inside the tank. But for most folks, the effort to keep them clean is simply too much work and constant attention to make it worth while. It's just much easier to keep a mental track of how much water is going into the tank and then dumping when you "feel" it is full.

There are several signs to indicate when it's time to dump. I use sound. This works well if your commode drops directly over the tank. After pushing the pedal you can hear the sound of the water splashing in the tank. The pitch will get higher and higher. After a while, you'll know what the sound is like when it's time to dump.

Some folks dump on a regular basis, ever 2 days, once a week, at the end of a week-end trip. Dumping on a schedule works and if you are constantly mindful you can approximate when it's time to dump.

We almost always camp with no sewer hook up. I use a Barker blue sewer tote that has a capacity of 32 gallons. My black tank has a capacity of 50 gallons (I think) If I overfill the tote when I dump, it can make one awful messy, nasty, stinky, embarrassing "mess" on the ground. So, I make sure I dump my black tank below my 32 gallon threshold. For us, every 2 to 3 days works and works well. I also account for the grey tank in that 32 gallons because I use the grey tank to back flush into the black tank to help clean it out better.

Backflushing also helps keep the tank cleaner and can help clean off the sensors too. Backflushing is possible by attaching a 3rd slide valve on the end of the sewer outlet where the black and grey tanks discharges. The black tank is drained completely first. Then the 3rd valve is closed and the grey valve is opened allowing the grey water to fill the black tank, backwards. Close the grey valve after the tanks equalize and open the 3rd valve again to drain the black tank. Depending on how much water you have in the grey tank, you can back flush 2 or 3 times and still have enough grey water to flush out the sewer hoses.

Back flushing pulls more "stuff".... especially toilet paper from the bottom of the tank that does not get swished out with the first dump. Removing the extra "crud" means less to potentially get stuck to the sensors.

Another technique for keep the sensors cleaned, as mentioned above in a prior post, is to add a few gallons of water to the tank when you travel. The sloshing will help clean off the sensors. And yes, this works.

Another technique is to use a toilet wand down the toilet, attached to a garden hose. The jet spraying out of the toilet wand will pulverize the inside of the tank. When the stream of water hits the sensors, it almost always knocks the crud off. But this is a cumbersome method, however it does work well.

Chemical down the toilet do very little to keep the sensors clean. Save your money and just squirt some Dawn dishwashing liquid, or some liquid Tide laundry detergent down the toilet. This will help your tank more than anything ... especially if it's been dumped, you've added a few gallons of water, and you are on the road traveling. The agitation will clean the inside like a washing machine. It works well.

Tank maintenance is something that does take constant attention. Eventually, you will develop your own technique that will work for you. But, experiment with them all until you find what works best for you.

[peanut]

I have the same issue - - after using this new fiver for a total of about three weeks since new.
Just returned from a one week trip where we had sewer hookup. So, for the final dump just before leaving I let the black tank drain for over twenty minutes. Nothing was coming out of the hose (clear elbow on it). The monitor said it was still 25-30 percent full.

New trailer. Never been used for #2. (we use the campground toilets for that since we are restricting our trips this first season while we become familiar with this new trailer. in other words, no boondocking yet). Only thing in the tank is water and #1. Wife (claims) uses very little TP and tosses it in a sealed container and does not put it in the tank.

Everyone can claim it is "stuff" clinging to the walls interfering with the sensors. Maybe, maybe not (at least in an older unit). I don't believe it with a new trailer. Never, even after 10 years, did I have this issue with our last trailer. I think it is probably sub-par components or sub-par installation or both. I think it going to be just one of those things I'll have to get used to and adapt to.

[RickV]

In 13 years of RVing and with 3 different 5vers I have learned that it is a waste of time and energy trying to make tanks sensors read correctly. Like a few others have posted "Learn your tanks". When flushing the "Terlet" when mine burps it is time to dump, on the other two it is time to dump when the DW says the tank is full while in the shower or doing dishes. One thing I do while draining the Black tank is after it drains and I have ran the flusher until it clears is to open the grey tank and do a 3 count and then close it. You'd be surprised what comes still comes out of the "Clean" Black tank. I do this a few times then have the DW fill the "Terlet" Bowl up to the top and dump it about 5 times again you'd be surprised at what still comes out.

[dutchmensport]

Originally Posted by RickV

... you'd be surprised at what still comes out.

That's exactly what back flushing from the grey tank does, except you don't have to use more water to do so. In a sense, you "recycle" the grey water for a second purpose. Backflush really pulls the "stuff" out without using more water.

Good point! Either way, a simple first time flush never gets everything out.

[Marblejunkie]

Lots of great comments heretofore. Did not see this one, but may have missed it.

Once the black tank is emptied, drop #20 lbs or so of party ice or crushed ice down the toilet into the tank. It will pile up as you add it in so have a stick or some tool to rake it aside to add the rest. Once you start driving, especially on curvy roads, the ice will slosh around in the tank and against the sensors, sometimes freeing them from whatever is sticking there. (Not always guaranteed).
I usually do this on the way home from a trip after dumping the tank, but it could also be done between hookups if traveling.

[fivergeezer]

You can try all the different holding tank cleaners made specifically for RV’s & when they don’t work try dumping a bag of ice cubes down the toilet after you’ve dumped & right before you pull away. The ice cubes will slosh around, scrubbing the residue off the sides of the tank. When you get to the next stop, flush & drain the melted ice & every thing should work fine. I f not, join the rest of us who just ignore the lights & dump more often. I’ve owned every type of RV since 1961 & never had the tank level indicators work properly after the first few times.
It’s easier to estimate the amount of water each flush uses compared with the capacity of the black tank & subtract an error correction, then dump before the level reaches the toilet flush valve.

[Jwaldrich]

Originally Posted by Joe1969

After draining the black tank completely, nothing more coming from the septic hose, the light shows 1/3 full. Galley and Grey drained and show empty. All other gages working correct. Any idea what may be causing this?

Pretty standard I'd say. Everyone I know has the same issue regardless of make or model.

[travelin texans]

Originally Posted by Marblejunkie

Lots of great comments heretofore. Did not see this one, but may have missed it.

Once the black tank is emptied, drop #20 lbs or so of party ice or crushed ice down the toilet into the tank. It will pile up as you add it in so have a stick or some tool to rake it aside to add the rest. Once you start driving, especially on curvy roads, the ice will slosh around in the tank and against the sensors, sometimes freeing them from whatever is sticking there. (Not always guaranteed).
I usually do this on the way home from a trip after dumping the tank, but it could also be done between hookups if traveling.

You'd do just as well to determine how much water those ice cubes melt down to & put that much more water into tanks with whatever chemicals, elixirs or potions you chose. Most likely the ice has melted before you got to the 1st curve in the road & added more water which is what it needs to begin with.
The ice cubes in the black tank is a myth! Dropping 10-20lbs of ice into a somewhat empty tank they'll fall to the bottom & lay there til they melt, they may slide back & forth scouring the tank bottom for 5-10 mimutes til melted. Or if added to a somewhat water filled tank, that 10-20 lbs of ice in a 35-50 gallon tank would like dropping a dozen ice cubes in 5 gallons of water.
But I guess if some feel it works then it won't hurt! It does add the needed water.

[sourdough]

Originally Posted by travelin texans

You'd do just as well to determine how much water those ice cubes melt down to & put that much more water into tanks with whatever chemicals, elixirs or potions.... you chose.

Reminds me of using "potion #9" on a black tank. "I held my nose, I closed by eyes...but it still stinks".... Sorry. It's a slow morning and I'm dragging my feet delaying getting out in this heat.

[dutchmensport]

Originally Posted by travelin texans

...
The ice cubes in the black tank is a myth! ...

That's exactly what ran through my head with the ice suggestion.

Watch this:

https://www.youtube.com/watch?v=iH6acEmqvcw

[flybouy]

I think the best use for ice is in a drink, especially while repeatedly flushing the tank. Personally, I find the ice most useful in a drink until I no longer worry about those lights or I just forget about it all together! YMMV