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Old 08-18-2019, 06:04 AM   #1
SiniWisdom
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Black Tank Flush

I have a 2018 Cougar 25RES and have been trying to clean the black tank with the flush valve on the side. After draining the black tank, I leave the valve open and connect a hose to the port. I then turn on the hose and wait for the water to come through the sewer hose. I was told that once it comes out relatively clear, the black tank should be cleanish. The problem is nothing comes out the sewer hose. The water is going in because there was a small leak in the connection (very small) so I know water was passing through the hose.

I went into the bathroom and raised the toilet seat to see if I could hear any water and nothing. Waited several minutes and still nothing coming out of the sewer hose. Is there something I'm doing wrong or do I need to get it looked at by a service shop (hopefully not)?

Any help is greatly appreciated.
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Old 08-18-2019, 06:12 AM   #2
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Where was the leak? the anti siphon valves are notorious for sticking or leaking. You need to find it and make sure it is operational. If not you can replace it with a new plastic one or upgrade to a metal one available at most big box hardware stores.

When I use the rinser, I will leave the drain valve closed for a few minutes to build up the water level in the tank, the MORE liquid you have the better the SOLIDS come out.
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Old 08-18-2019, 06:16 AM   #3
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Very common for the black tank flush line backflow/vacuum breaker valve to be installed backwards. It's usually located under the bathroom sink and can be easily disconnected and swapped around. They are also VERY prone to leaks so keep an eye on it.
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Old 08-18-2019, 06:38 AM   #4
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Where was the leak? the anti siphon valves are notorious for sticking or leaking. You need to find it and make sure it is operational. If not you can replace it with a new plastic one or upgrade to a metal one available at most big box hardware stores.

When I use the rinser, I will leave the drain valve closed for a few minutes to build up the water level in the tank, the MORE liquid you have the better the SOLIDS come out.
Sorry, I should not have mentioned the leak. It is simply like attaching a hose to an outside spicket without plumbers tape. I only mentioned it to indicate that I knew water was going through the hose. That is not the problem. The problem is that no water is coming out of the sewer hose.
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Old 08-18-2019, 06:45 AM   #5
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Very common for the black tank flush line backflow/vacuum breaker valve to be installed backwards. It's usually located under the bathroom sink and can be easily disconnected and swapped around. They are also VERY prone to leaks so keep an eye on it.
I will take a look at that and see if I can find it. I'm not sure I will know if it's on backwards or not. I guess I can Google it to see if I can find a image of the correct position. Does that valve allow water into the black tank for flushing purposes?
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Old 08-18-2019, 06:47 AM   #6
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It will be marked with the direction of flow need for proper operation. IIRC the bottom fitting is IN and the side fitting is OUT to the tank.
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Old 08-18-2019, 06:57 AM   #7
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One more question: if it was on backwards and I ran water through the black tank flush port, would it cause black water to run into the fresh water lines and hence have black water coming through the faucets? If not, where did that water go that I ran through the port?
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Old 08-18-2019, 07:00 AM   #8
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The black tank rinser is a COMPLETELY SEPERATE water line from everything else. No way to get any water from that into your fresh water system. If it was backwards, water simply wouldn't flow. Where it went I have no idea unless it wasn't flowing. Did you put your ear to the hose at the fitting and hear water flowing? when you unhooked the hose water probably came out because the valve is normally at a higher point than the inlet and gravity will cause it to flow back out of the line.
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Old 08-18-2019, 07:02 AM   #9
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The black tank rinser is a COMPLETELY SEPERATE water line from everything else. No way to get any water from that into your fresh water system.
So where did that water go?
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Old 08-18-2019, 07:08 AM   #10
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Did you see or hear water running when looking down through the toilet?
I suspect the valve is backwards or just broken & no water going into the tank, just because the water is turned on to the hose doesn't mean it's flowing.
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Old 08-18-2019, 07:17 AM   #11
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I will take a look at that and see if I can find it. I'm not sure I will know if it's on backwards or not. I guess I can Google it to see if I can find a image of the correct position. Does that valve allow water into the black tank for flushing purposes?
Look closely at the picture, it has an arrow showing flow direction. But it doesn't really matter because it's installed backwards so just swap it around. Without getting into the underbelly you can't tell which hose is coming and going. Chuck can probably verify this but it's one of the most common issues people have and it would be such a simple problem to correct at the assembly line!
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Old 08-18-2019, 07:25 AM   #12
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Cruiser RV is notorious for that!!
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Old 08-18-2019, 10:18 AM   #13
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It will be marked with the direction of flow need for proper operation. IIRC the bottom fitting is IN and the side fitting is OUT to the tank.
Chuckster- does that mean the flat part of the fitting should be "up" (based on the pic Steveo posted?) That would indicate which leg is bottom and side. (hope that makes sense)!
Thanks!
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Old 08-18-2019, 10:20 AM   #14
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Yes, the flat top is “the top” and it should be in that position when installed.
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Old 08-18-2019, 10:22 AM   #15
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-Chuckster- Thanks!
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Old 08-20-2019, 02:38 PM   #16
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I have a 2018 30 RLS Keystone Cougar. The black water flush wouldn't work, problem was the water lines were hooked up backwards on the check valve. I had to switch them & it works now. Thanks to this Forum for advice as to where to find the valve.
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Old 08-20-2019, 03:02 PM   #17
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I flushed mine the other day. Had some time so I gave it time to build up and wash as much of the tank as I could. I was checking the content flow coming out through the clear fitting at the hose end when I notice the toilet paper just hanging in the end. Upon further inspection and after I stopped the flow I tapped the hose end on the concrete near the drain. A piece of OSB board fell out that was in the shape of a crescent moon. Looked to be about the same diameter as the toilet base. Guess the guy at the factory just cut it open to install the toilet,watched the piece fall and then went to lunch. I got lucky I was able to float this piece of scrap out without it getting caught in my pipes. Who was it that said you will find "surprises" in your rig well after purchase?
He was right.
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Old 08-20-2019, 05:47 PM   #18
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You've found "half the black tank surprises"...

The OSB is the floor above the black tank, still to come is the black tank "circle" where they cut the opening. If one was in your tank, chances are pretty good that the other is still floating around in there... OSB will eventually waterlog and separate into smaller chunks. The plastic "roto-cast" tank section, well, it's as durable as your tank walls....

You've got more to come, keep watching......
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Old 08-21-2019, 08:01 AM   #19
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I have a 2018 25RES and they installed the valve backwards. On our model it is under the bathroom sink. I pulled the valve and installed it correctly. Works great now.
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Old 08-21-2019, 02:21 PM   #20
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Steveo- When saying the black tank flow vacuum/breaker are prone to leaking, does that mean they should be replaced after so many years? Do they eventually fail or if they don't leak now, they won't leak because it's poor installation that causes them to leak?
Thanks!
-Andy
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