So we took our new to us 5er out on it's maiden voyage to a campground with full hookups about two hours from home. I check the tank levels the morning after our late night arrival and all the tanks were showing one light. I figured that was normal. But the black tank was already showing 2/3 full. That can't be possible. It's only been used maybe three times. So I look in the commode and there's already a pile forming. So I use the black tank flush, and I stick a hose down the commode to break up the pile. After a while I open up the valve and I get good flow. (I have a clear plastic connector so I can monitor the flow) After awhile I get somewhat clear water coming out. I shut off the flush and wait for the flow to stop and I look in the commode again. It still has about an inch of water in it. I check the level again, and now it's down to one light. Ok, cool. But I shouldn't have any water in it.The next day, after the toilets been used a few more times, I'm back up to 2/3 full. There's no way I could have paper hanging on the sensor. I flush it again, and again I get good flow, clear water, and there's still water in it. Why is the reading so far off and how do I completely empty the tank? How do I tell when I really need to empty it on extended stays?

Hi,The tank sensors are notoriously unreliable. Most of us pretty much ignore them.

Waste tank drains come out the side of tank....so there is a lip and will always be a little water in bottom after draining.Also some black tanks have a 'sloped shelf' right were toilet dumps. If not using at least a full toilet bowl of water and then let water run a couple seconds after flushing poop pyramids will build up quickly.OEM tank sensors are just a bung-stud that stick thru sidewall of tank. Doesn't take much to cause them to register.I haven't looked at my level monitors in years.Toilet 'burps'......time to dumpSink/shower starts to drain slower...time to dumpWater pump goes 'burrrrrrp'........should have put water in fresh tank :S

You have already discovered the only reliable way to determine the level in the black tank - open the toilet drain valve and take a look. A flashlight is often helpful in doing this. Just don't drop it into the tank.

Welcome to the world of RV-ing! False black tank readings are unfortunately normal. The button sensors can get slime built up on them, and in some tanks, the 1/3 sensor can be a bit too low which can make it worse. Thorough cleaning at each dumping will go a long way to reducing false readings. Fill tank to near full before dumping. If you have a built-in tank flusher, let that run for maybe 5 minutes then fill the tank again and dump. Look down into toilet (water turned off) and if not clean on the bottom, repeat the above process again. I can get our tank spotless doing that. We replaced the standard button sensors with Horst Miracle probes and along with thorough cleaning, we don't get false readings now.Also, before each use of the tank, add 4-5 gallons of water and don't skimp on water with each flush. That is, unless you are somewhere like Cali. where there is a water shortage. If there isn't enough water in the tank, you will end up with a build-up of solids that will be harder to flush out and clean.Chemicals before each use of the tank may help a little but it's not usually in the tank long enough to break down the solids.

Your next phase of ownership is developing your sense of black tank level. It's a skill that's developed by paying close attention to use habits, noises, if you use other toilets such as campgrounds and not use your rig etc.So in short just give up, you are the monitor. Welcome to the club brother. :)

Black Tank Readings Not Possible | Good Sam Community

23 Replies

wcjeep
Explorer
Aug 24, 2014
My first truck camper was a late 70's Vacationer. The tank sensors were still accurate when I sold it. My 2008 AF811 I bought new has terrible sensors.
old_guy
Explorer
Aug 24, 2014
if you are seeing a pyramid building in the tank then you either did not start with any water in the tank and or not using enough water to flush.
Nomadac
Explorer
Aug 24, 2014
Dutch_12078 wrote:
I've installed the SeeLevel II external capacitance tank sensors and display system on each Class A we've owned, and found them to be reliable, accurate, and relatively easy to install. The percentage readouts give a much better picture of the tank status than the "Empty, 1/3, 2/3, Full" systems common to the "screw through the wall" sensor systems.

X2 We have the SeeLevel system that gives the reading in %filled, i.e 23%, 45%, etc. than you use the tank capacity to determine the gallons in the tank. When my tanks are empty they read 0%.
It also gives battery voltage, propane tank reading, fresh water, black and gray tank readings, that are all very accurate.

This is the only accurate system to have IMO.
Nomadac
Explorer
Aug 24, 2014
Dutch_12078 wrote:
I've installed the SeeLevel II external capacitance tank sensors and display system on each Class A we've owned, and found them to be reliable, accurate, and relatively easy to install. The percentage readouts give a much better picture of the tank status than the "Empty, 1/3, 2/3, Full" systems common to the "screw through the wall" sensor systems.

X2 We have the SeeLevel system that gives the reading in %filled, i.e 23%, 45%, etc. than you use the tank capacity to determine the gallons in the tank. When my tanks are empty they read 0%.

This is the only accurate system to have IMO.
Nomadac
Explorer
Aug 24, 2014
Dutch_12078 wrote:
I've installed the SeeLevel II external capacitance tank sensors and display system on each Class A we've owned, and found them to be reliable, accurate, and relatively easy to install. The percentage readouts give a much better picture of the tank status than the "Empty, 1/3, 2/3, Full" systems common to the "screw through the wall" sensor systems.

X2 We have the SeeLevel system that gives the reading in %filled, i.e 23%, 45%, etc. than you use the tank capacity to determine the gallons in the tank. When my tanks are empty they read 0%.

This is the only accurate system to have IMO.
Dutch_12078
Explorer III
Aug 24, 2014
I've installed the SeeLevel II external capacitance tank sensors and display system on each Class A we've owned, and found them to be reliable, accurate, and relatively easy to install. The percentage readouts give a much better picture of the tank status than the "Empty, 1/3, 2/3, Full" systems common to the "screw through the wall" sensor systems.
Acampingwewillg
Explorer II
Aug 24, 2014
I did use one of those "wands"....no, not the Rv wand but one from Costco that is made for cleaning gutters( very good spraying force). After a full cleaning my sensors did read empty for the first time in years. Of course its a pain to use in the mh so it doesn't get that good cleaning often.
Oasisbob
Explorer
Aug 24, 2014
Holding tank readings are about as trustworthy as politicians or RV sales persons. . O well Any inventers out there who can come up with some better way?
azrving
Explorer
Aug 24, 2014
Your next phase of ownership is developing your sense of black tank level. It's a skill that's developed by paying close attention to use habits, noises, if you use other toilets such as campgrounds and not use your rig etc.

So in short just give up, you are the monitor. Welcome to the club brother. :)
myredracer
Explorer II
Aug 24, 2014
Welcome to the world of RV-ing! False black tank readings are unfortunately normal. The button sensors can get slime built up on them, and in some tanks, the 1/3 sensor can be a bit too low which can make it worse.

Thorough cleaning at each dumping will go a long way to reducing false readings. Fill tank to near full before dumping. If you have a built-in tank flusher, let that run for maybe 5 minutes then fill the tank again and dump. Look down into toilet (water turned off) and if not clean on the bottom, repeat the above process again. I can get our tank spotless doing that. We replaced the standard button sensors with Horst Miracle probes and along with thorough cleaning, we don't get false readings now.

Also, before each use of the tank, add 4-5 gallons of water and don't skimp on water with each flush. That is, unless you are somewhere like Cali. where there is a water shortage. If there isn't enough water in the tank, you will end up with a build-up of solids that will be harder to flush out and clean.

Chemicals before each use of the tank may help a little but it's not usually in the tank long enough to break down the solids.

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Black Tank Readings Not Possible

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