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Old 12-28-2018, 10:24 AM   #1
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Black water tank

After emptying our black water tank, it still registers 1/3 full. Why and what should we do?
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Old 12-28-2018, 10:28 AM   #2
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After emptying our black water tank, it still registers 1/3 full. Why and what should we do?

Those tank sensors are notoriously inaccurate. There is probably remnants sticking to the tank walls giving you a false reading. Try filling your black tank with water and emptying it a couple of times to rinse it out.
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Old 12-28-2018, 10:39 AM   #3
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After emptying our black water tank, it still registers 1/3 full. Why and what should we do?
Curious as to what others will say after I post this, so chime in please.

My father always did this in his motor-home/s, he would buy orange scented cascade and add it to his tanks along with about 5 gallons of water after dumping... then he would drive home or wherever he was heading with that in there just churning away. Not only would it clean everything (sensors included) but it would smell nice too!

I do this and to this day I haven't had any issues.
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Old 12-28-2018, 10:46 AM   #4
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Also if possible next time you travel dump a bag of ice cubes down the toilet. As you drive/tow the camper to the campground the ice will bounce around inside the tank and this will help clean the tank walls. After arriving drain the tank, the sensors should read empty than. But the waste paper will cling to the sight gage again from use.

I use plenty of water and flush the tank almost every time I empty, but the gage will still register 1/3 full sometimes. I just live with it and when the monitor reads full is when I will empty. The full and 2/3 monitor usually will show empty when I am finish dumping so, to me that is all that matters.
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Old 12-28-2018, 10:48 AM   #5
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Also if possible next time you travel dump a bag of ice cubes down the toilet. As you drive/tow the camper to the campground the ice will bounce around inside the tank and this will help clean the tank walls. After arriving drain the tank, the sensors should read empty than. But the waste paper will cling to the sight gage again from use.

I use plenty of water and flush the tank almost every time I empty, but the gage will still register 1/3 full sometimes. I just live with it and when the monitor reads full is when I will empty. The full and 2/3 monitor usually will show empty when I am finish dumping so, to me that is all that matters.
The ice doesn't damage the sensors?
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Old 12-28-2018, 11:40 AM   #6
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If you are staring at sensors hoping for a correct answer it ain't gonna happen. But Wait, there is an easy way.

1) Know the capacity of your black tank in gallons

2) Most of the fill in the black tank comes from sitting down, thus, how many people sit down daily.

3) What is the volume of the Royal Flush.

Just a bit O math and you can easily figure your fill rate.

TIP: Open your Black Tank first or have someone open it for you as you watch it empty and time it in its 3 stages: Full hose flow, half hose flow, trickle, stop timing at the trickle.

Grey tank: = 3 showers them dump works for us, unless I shave (in the shower) and it will start to back up into the shower every so slightly.

Galley tank we dump upon leaving or after 4 or 5 days, but we eat out lunch and dinner mostly.

Most would be better off if they covered over the tank(s) read outs.

NOTE: I have NEVER had a backup or over full tank unless I shave in the shower...
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Old 12-28-2018, 12:04 PM   #7
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Dawn dishwashing liquid 1/2- 1 cup, then drive. Empty and rinse. May have to do it several times. Keep dump valves lubeed.
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Old 12-28-2018, 12:32 PM   #8
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You should begin to totally ignore the sensors forever. There are 10,000 methods to make them work. Nine or seven of them might even work on a rare, good day.
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Old 12-28-2018, 01:01 PM   #9
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I must confess... I have no idea if my tank sensors work or not... I have never tried them. We have only had the black tank fill once as we usually camp 2-3-4-5 days at a time. We shower in the shower house. I think you will learn how full it gets by the sound of the water when flushing.
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Old 12-28-2018, 06:07 PM   #10
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Also if possible next time you travel dump a bag of ice cubes down the toilet. As you drive/tow the camper to the campground the ice will bounce around inside the tank and this will help clean the tank walls. After arriving drain the tank, the sensors should read empty than. But the waste paper will cling to the sight gage again from use.

I use plenty of water and flush the tank almost every time I empty, but the gage will still register 1/3 full sometimes. I just live with it and when the monitor reads full is when I will empty. The full and 2/3 monitor usually will show empty when I am finish dumping so, to me that is all that matters.
Ice cubes dont really help

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Old 12-28-2018, 07:07 PM   #11
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... My father always did this in his motor-home/s, he would buy orange scented cascade and add it to his tanks along with about 5 gallons of water after dumping... then he would drive home or wherever he was heading with that in there just churning away. Not only would it clean everything (sensors included) but it would smell nice too! ...

I've been doing that from day one, just over five yrs, ... using the cheapest laundry detergent I can find(sometimes will include Calgon Liquid water softener) and 4 to 5 gals of HOT water, ... it sloshes on our way home, ... if we're going out again soon, I'll just let it sit(it is a holding tank), ... if we've no soon trips planned, I'll empty that into our septic tank at home, ... but none of that is for the sensors, I ignore them, ... that's just my tank cleaning routine,and it works, ...
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Old 12-28-2018, 07:23 PM   #12
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X2, It's NOT the floating stuff, its all settles to the bottom, best thing is a few hours of slosh using a CHEAP liquid soap. Some soaps are grease cutters and that is not what you want. But works GREAT in Grey and Galley tanks...


They (ice cubes) do work in a sink disposal, will clean it like new.
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Old 12-28-2018, 08:15 PM   #13
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As others have stated, the stock tank sensors are pretty worthless except maybe after a really good tank flush, possibly with a spray wand down the toilet instead of the built in tank flush.


That said, on my last two campers, I've had significantly better accuracy by installing Horst Miracle probes in place of the stock sensors. I almost always get an empty reading on my gauge. Maybe not immediately after using the black tank flush, but almost always within 10 or 20 minutes after dumping and using the black tank flush for a few minutes.


Here is a video showing how the stock sensors read poorly and the difference in the Horst Miracle probes.


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Old 12-29-2018, 01:31 PM   #14
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We've found that our tanks don't completely empty when we are level. It's not a big deal when we are at an RV Park.

I tilt the 5w over some when we leave the park and I get several gallons from each tank.
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