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drillagent's avatar
drillagent
Explorer
Aug 24, 2014

Black Tank Readings Not Possible

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?

23 Replies

  • 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.
  • 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 dump
    Sink/shower starts to drain slower...time to dump
    Water pump goes 'burrrrrrp'........should have put water in fresh tank :S
  • Hi,

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

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