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Old 01-11-2022, 12:38 PM   #1
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Join Date: Aug 2021
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Black Tank Issue

I'm trying to determine if the black tank's knife valve is broken, or stuck, or if the tank is just clogged.

There's still a lot of resistance when opening and closing the push rod, but not even a drop of water runs into the sewer hose.

I've tapped on the blade housing lightly with a hammer to see if it can get unstuck, but that didn't do anything. The valve is just out of the way of the underbody access panel, enough that I can't get any tools in, except probably a ratchet to undo the 4 bolts. But the tank is full, so I need to drain it first.

What does a broken valve feel like ? How can I tell if it's broken or stuck or clogged, without just opening it all up and dumping sewage everywhere ?

I've been researching for a few hours, trying what I find online, and haven't made any progress.

Anyone have any tips or ideas ?
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Old 01-11-2022, 01:25 PM   #2
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Location: Bend,or
Posts: 181
I recently had a similar issue.
I used a sewer connection that you connect a garden hose to, and allows for back flushing the system.
With the hose on, it was easier to work the valves since pressure was equalized.
My problem seemed to be a clog, as it eventually let loose while back filling.
I got my adapter at a local Ace Hardware.
Make sure someone is inside checking for flow up the toilette!
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Old 01-11-2022, 01:25 PM   #3
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It feels like the handle doesn't move at all the valve may be stuck. If it's not frozen and it is moving free (resistance is ok fine) then your tank is likely clogged in the worst possible condition.

Recommendation #!

This will allow you to safely troubleshoot. Throw that on (close it) then open the original. You can then move on to recommendation #2 and that is a drain snake from the topside to get past the gate valve hopefully. If you are clogged then you have to physically break it up. They make all sorts of flushing things from the outside, or the inside but if it's really clogged and full then it's back to basics. Lots of tricks with hot water blah blah but sometimes you are in a bad spot. You can also consider getting a septic service to pump you out if you can't get it.

I created an adapter that allowed me to run a snake from the drain pipe side, with a cap on the end to prevent exfil. That didn't work. I went to a spot where I could hook it up and work on it with the pipe open and a clear adapter. One guy watching while I ran a power snake and then viola.

Then, I filled a 5 gallon bucket with water and dumped it into the toilet again and again and again while my observer commented on size, color, speed of exfil lol.
What a chore. This was all due to the previous owner not taking care of business so to speak.
The wetter you keep your tank the better so then when you are driving down the road it sort of agitates itself. Another trick is dump a bunch of ice in before driving. That is supposed to sort of scour then melt. Anyway none of that is going to help you with the current issue.

Anyway good luck soldier. PM me if I can help, what an odd thing to be an expert in huh
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Old 01-15-2022, 06:45 AM   #4
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Location: So Calif
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You most likely have a clog or pyramid in the tank.

Is this a ORV trailer? Your profile doesn't give any info for us to guide ypu accurately. You state the tank is full....Is this tank drained on a reqular basis?

You may have to drop the coroplast to find the location of the valve. Or you can cut a 3 sided access hole/door to check it out, then tape it up with Gorilla tape

Be careful you don't break the valve and create a hazmat situation.

Sometimes a experienced tech needs to get involved to be sure this does not become a nightmare. They can pump the tank from the toilet if needed.
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Old 01-17-2022, 11:47 AM   #5
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Thanks for the responses everyone. We thought we were making progress, but turns out no, so we're still working on using our tankflush to get it done. I'm going to pick up a backflush adapater later on today.

iceclimber, those are some good tips, but I'm not quite there yet. Going to try a normal backflush first, since we've made SOME progress. We're currently parked on my dad's land hooked directly into his septic, and we're here for a few more months, so location and time are on our side.

egwilly, yes, it's an Outdoors RV 23RBS. I've gone underneath and opening up the underbody stuff and looked at the valves and the plumbing, but you can't see inside the pipes and tanks so it didn't help any.

The tank is drained regularly, and we make sure to use lots of water when flushing. We're thinking the valve is failing, maybe letting a small stream of water by so the tank "dried up" somehow. I'll be replacing both knife valves for the grey and black tanks, but need to get them empty first for sure.
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Old 01-20-2022, 08:33 AM   #6
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The flushking is the way to do it.
It puts your gate at the opening.
Then you can open the rvs gate
Without spilling also you can back
Flush your gate valve to see if its plugged.
If my flushking failed id go out
And buy another ..
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Old 01-21-2022, 03:48 AM   #7
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Location: Rendon, Texas
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A few of my thoughts.

To determine if the valve is closed, I would send a fish tape up the lines until it hit a barrier. Then withdraw the tape and measure it to determine if it reached the approximate location of the valve. If it did, then the valve is still closed.

I wonder if a septic tank service could suck out the yuck after you removed the toilet. Worth a call.

If you have to cut the line, it will get messy. Have large buckets available or dig a large hole in the ground, position the valve over the hole, and then cut the line. I don't know if a repair shop will help with this or not. Call them for advice.
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black tank, tank

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