Faulty black water sensor

I just installed the See Level sensors on our 2002 fifth wheel. We camp for about 3 months of the year where we do not have sewer hook up but we do have water and electric. The OE readout has never worked (we bought this unit 6 years old). Our toilet drain has a dog leg so you can not see down into the tank so by the time you see water you are full or plugged. My wife is always asking how much room do you think I have, am I going to run out of water while your fishing, is it safe to do dishes???
Not anymore..I think it is going to eliminate a lot of uncertainty.
I will say that because our tanks are around 8"tall and you have to cut the sensor strips to fit tank, that the percent readings we get jump in 6% intervals, not 1% as I would like but that is 16 different levels of full rather than 1/3rds.

Basically there is an electrode at the bottom of the tank and 3 more going up the sides. When the water reaches the level of another electrode, it creates a circuit between the electrodes...that circuit is tied to the little lights you see.

Works fine with fresh water tanks but with sewage, scum gets stuck to the walls and wicks up water, so the circuits become semi-permanent.

You can mess around trying clean the walls but really more hassle than it's worth.
- For weekends or a longer trip where you move around, just drain before driving.
- If you will be somewhere for a while with a sewer site, just open the drain for a couple minutes every few days (don't leave it open as it causes other issues).

Only place that would be a bit of an issue is if you are staying for a week or more someplace that doesn't have sewer. Then you either need to use a blueboy or haul the trailer up to the dump station. Given some experience, you should develop a good idea of how long you can go between dumps.

False readings are normal. In fact, if you don't have them, something is very wrong! :) Many ignore the basic level indicators and learn to know when the tank(s) need dumping.

You can flush, rinse and use chemicals and get a tank back to factory fresh, factory clean condition but it won't take long before the false readings are back. RV manufacturers shouldn't waste money on installing this type of level indication and should install something that actually works (like SeeLevel for ex.).

Always dump, flush & rinse your black tank as best as you can. Add a few gallons of water before using the black tank, don't skimp on water when flusing and fill the tank as high as possible before opening the dump valve. Then use a down-the-toilet wand, backflush elbow and/or in-tank rinser to get it as clean as you can. This will help to restore correct readings, but not always back to empty tho. Sometimes the sensors can be in a location where water spray can't get to them very well.

I added a shutoff valve behind our toilet so I can peer down into the tank to see how clean the bottom is and not have to go out and shut off the faucet at the pedestal. I let our in-tank rinser run for 10-15 min. while breaking camp. Once or twice a year I use a little Liquid Drano along with a little water and drive around a bit to let it slosh around (Liquid Drano won't hurt metal or plastic and our owners manual says to use it). Doesn't take long for false readings to return though (sigh)... :(

You could replace the sensors with a Horst Miracle probe. These can really help sometimes. They worked great on a previous TT but after installing them in our current TT, don't really help at all. Depends a lot on the shape/configuration and dimensions of a tank (there are many different ones).

Standard "button" sensor and mounting location on a tank and also a Horst Miracle probe.

DutchmenSport wrote:
Assuming this is a new camper for you, in time you'll quit using the sensor readings completely. Why? Because in time, you'll know how much water you can use, and as you get more familiar with the camper, it just becomes second nature to keep a mental track of how often things get used, especially water usage. You'll just know when it's time to fill the fresh water tank and dump the holding tanks.

As far as the black tank goes, most camper have the toilet with the foot pedal and the slide valve in the bottom of the bowel. Every time you push that pedal, you can look down the hole and see how full the tank is. Here again, it takes a few times to learn it, but it does happen.

I very seldom use my sensors any more, but after 5 years of owning this camper, the original factory sensors still work. I attribute that to towing the camper with little water in the black tank and the dish washing liquid. And I actually tried them last night, and still work (showing empty right now, which it is.)

good advice here

over time you will learn how many days you will average on both black and grey tanks. especially if the same number of people camp with you trip by trip

always just my wife and i so i always can judge pretty close to accurate.

always good advice to never dump black tank until its 3/4 full to full and always start a trip with some water (i usually pour about 4 or 4 gallons in the black tank before we leave home for a trip)

We have never had an RV with working sensors for black water! Too many ways for it to be useless! Don't worry about it. As everyone else has stated, you can tell just by looking. Others have also said you will "get to know" how long you can go before you need to clean out the tank. Just takes experience. The wand is useful - we use it whenever we dump. Still doesn't usually clean off the sensors, but gets the tank very clean.

Anyone else notice that you can also hear when the black tank is getting full? The sound of the flush changes like blowing into different length straws.

DavinD wrote:
Anyone else notice that you can also hear when the black tank is getting full? The sound of the flush changes like blowing into different length straws.

Actually yes, but it must be an unconscious thing, because I really never thought about it. After you mentioned this, yes. It's usually the sound that gets my attention to look in the hole.

Absolutely 100% dead on with this! Thanks for waking up me up from an unconscious state of mind! :B

I've never heard of black tank sensors that have worked consistently after the first use. Occasionally, if the tank gets hosed out especially well AND the owner is very, very lucky, that sensor will be accurate. Once. Next use, though, and they fail again.

This has all been such great advice! Of course, you know We’re new to RVing just by the question that everybody seems to know about. And now We do! I ordered a wand, got some new hearing aid batteries and I plan to wear my glasses when I flush. But most of all I learned it it’s not anything to worry about and that’s the real gift you all have given us. Thank you so very much for being such a great group. This kind of help makes us feel we are not alone with a strange beast!

DavinD wrote:
Anyone else notice that you can also hear when the black tank is getting full? The sound of the flush changes like blowing into different length straws.

Lol, add to that standing and watching all the "stuff" flow out through a clear elbow. Besides letting you know how empty the tank is getting, it's weirdly mesmerizing and entertaining... :C