Black Water Tank Level Sensors Screwy

[GodsJarsOfClay]

In my first year full time on the road and have a persistent, possibly worsening issue with the black water tank. Specs on my 2020 Rockwood 2706WS (33 ft) say I have a 45 gallon black water tank. (Tech at dealer says it's much smaller). I always put in 4 caps of Tank Digest with a gallon of water to start and have inconsistent reading on my panel so can't tell level of liquid in tank. I've used the tank-wash/flush inlet for from 15 minutes to 2 hours. Filled the bowl multiple times for a "push" flush (valve open of course). when dumping, water starts to run clear within 5 minutes or less. It never reads empty, goes from 1/3 to 2/3 after 6 quick pees with minimal flush water. It can go for 4 days with 2 people using it, never reads full, but when "testing" to see if full light comes on, had sewage seeping from under toilet before indicator light shows tank is full. This issue has persisted from the time I first started using the camper. I will try putting a bag of ice down the shoot next timer I move to help dislodge any paper stuck on the sensors. Would like to avoid pulling bowl, opening underbelly and dropping the tank for visual inspection. Any similar experiences or suggestions?

[Cabinfever97]

I never trust the indicators, not even on a new TTs maiden trip. I keep an ear and eye when flushing. I can tell by the sound when the tank is getting full and with a flash light can see as well. Remember the tank is not very high. It gets its volume by the length and width. I flush the black tank a bunch as well. Not to keep the indicators working but to be sure the solids are gone and do not build up.

[boondocking]

Next time you dump the tank put in a cup of Calgon (mixed with 1/2 gal of water) and 1/2 cup of laundry detergent. That will help clean the sensors while you are driving around.

I do that after every third to fourth dump and my sensors stay accurate.

[GodsJarsOfClay]

Thanks for the advice. Last time we broke camp we only drove a few miles to the next camping grounds. We did throw in a bag of ice, some Downy and some Dawn, (although probably not enough) along with an ounce of digest. Not much chance to get it all to swoosh around. It looked like it was a little better, but not really. I'll try your brands and quantities (proven history of success) on our next move which will be at least a 3 hour drive so I'll get more swooshing action then.

[GodsJarsOfClay]

My ears are'nt very pitch sensitive. When testing to see if "full" indicator came on, ended up with sewage leaking out from under toilet. Still couldn't see any liquid down the hole - just assumed it had overflowed. Could I have another problem there as well? There is no leakage when using the toilet - was only after about a week (just 2 of us).

[Adrian Gordon]

My experience is that if your tank sensors (especially your black tank sensors) are working correctly, it is only because the Gods on Mount Olympus are too busy screwing up somebody else's day to bother with you. Don't worry, they will eventually get back to you, probably sooner rather than later.

[DouglasReid]

This will be tedious but it will confirm the volume of your tank.

1. drain the tank completely.
2. get a 5 gallon bucket fill it and pour the water into the toilet.
3 after each bucket full look at the sensors to see what the reading is
4 do this until the tank is full (water running on the floor would be a good indication or you should be able to see it when the ball valve is open by looking down into the toilet)

The sensors are notoriously unreliable for a number of reasons, The location of their placement on the side of the tank is one reason for their inaccuracy.

If it never reads full I would suspect that particular sensor's wire is broken or off the contact on the outside of the tank.

[Scrapper]

Originally Posted by GodsJarsOfClay

My ears are'nt very pitch sensitive. When testing to see if "full" indicator came on, ended up with sewage leaking out from under toilet. Still couldn't see any liquid down the hole - just assumed it had overflowed. Could I have another problem there as well? There is no leakage when using the toilet - was only after about a week (just 2 of us).

Sounds like you have the infamous Dometic 300 toilet. They are made from sections of plastic fitted together that have a record of leaking or smelling badly. Call Dometic and ask for a 310 series toilet which is an almost direct drop-in replacement.

The toilet will burp when your black tank gets near full while you flush it.

Always start with 5 gallons of water in your black tank along with the chemical of your choice. Anything less is not enough to slosh onto the sensors while driving.

[LannyCox]

Count me among those who have never had an accurate reading of my Black Tank level in my Class A. In addition to having the tank level indication problem, it also affects the operation of the Thetford electric toilet in the main bathroom. When the Black Tank level indicates full, a signal is sent to the Thetford toilet preventing it from flushing!

The lowest level on the Black Tank I have ever seen is 1/3 full!!

[JACA]

The #1 Rule that all RVers should learn:

Never, ever trust any tank level sensor/indicator lights.

I've had 4 different RVs - none of the tank level indicators were ever accurate enough to trust, even when they were brand new. At best, they might give you a ballpark figure - somewhere between empty and full.

[BDenn]

I have a 2019 Class C. I started taking showers in it last year. I found my grey water sensors did not work well. I went to all the connections and found them loose and corroding. I cleaned them all off using dermal wire brush a little Dielectric grease. I then went through black water sensor wires. found wires loose. They worked well for the rest of the season. I also went through all the grounds I could find. Shaking my head at all the loose grounds I found that started to corrode. Esp. the generator ground.