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Old 04-19-2011, 04:28 PM   #1
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Black Tank Flushers...

The factory-installed black tank flushing system on our 8315BSS has a warning sticker on it that states the drain valve must be open when using the system. Does anyone know why this is? Seems to me that it would operated more efficiently if the tank was partially filled (say 1/3 or so) and then the drain valve opened, once or twice, to allow the "rush" of water to do it's thing. Followed by a rinsing with the valve open until the water runs reasonably clear. Just wondering if it would work better this way.

...VTX-AL
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Old 04-19-2011, 04:34 PM   #2
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I believe it's in case someone leaves it unattended. You could have some problems if you over filled the tank!
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Old 04-19-2011, 05:01 PM   #3
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Quote:
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I believe it's in case someone leaves it unattended. You could have some problems if you over filled the tank!
X2 - That is what I have heard too.
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Old 04-19-2011, 06:11 PM   #4
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Here is what I learned, that the valve thats in the water supply line prior to the black tank is a one way valve. If water starts to back up in the line from the sprayer it automatically shuts the valve off so no water is going in the tank. The reason they recommend leaving the tank gate valve open is because the sprayer in the tank is not far off the bottom, so it wouldn't take long before the water level inside the tank starts to back up into the service line towards the oneway valve and shuts its off...

Here is a link that has a bunch of info:
http://www.forestriverforums.com/for...ion-11087.html
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Old 04-19-2011, 06:19 PM   #5
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Here is what I learned, that the valve thats in the water supply line prior to the black tank is a one way valve. If water starts to back up in the line from the sprayer it automatically shuts the valve off so no water is going in the tank. The reason they recommend leaving the tank gate valve open is because the sprayer in the tank is not far off the bottom, so it wouldn't take long before the water level inside the tank starts to back up into the service line towards the oneway valve and shuts its off...
Bill,

That check valve is between the black tank and the outside hose connection; not your fresh water tank. The one way check valve is so contaminated water does not (supposedly) get into your water hose.

What others have said is correct; the water pressure on the sprayer will quickly fill an already partially full tank and make a mess if you are not right there opening and closing that gate valve. Getting the timing wrong, or getting distracted will cause a smelly geiser out the top of your vent stack (potentially bursting your black tank).
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Old 04-19-2011, 06:59 PM   #6
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Lou, that's what I meant by the supply line which feeds the black tank sprayer, sorry if it was a little confusing...
However, correct me if I am wrong, but if you keep your gate valve closed on the tank and let the sprayer basically fill your tank for you. One would think that the water would create a resistance in the line causing the one-way valve to close stopping water from going into the black tank. I thought that was the purpose of the check valve in the water line.
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Old 04-19-2011, 08:45 PM   #7
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The check valve is to prevent water in the tank from being forced into the hose; not the other way around. If the check valve was reversed, water would not flow into the tank, but be stopped by the check valve.

When you remove the hose from the outside bib, the water that was trapped between the check valve and the hose bib will run out. The check valve will prevent water from the tank from entering the hose and siphoning poo out.
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Old 04-19-2011, 08:51 PM   #8
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I think that the pressure from the hose would be greater than any built up pressure in the tank allowing the tank to continue filling and potentially over filling.
I would also think that if the pressure in the tank did somehow happen to build up to point that it equaled the pressure from the hose that everything would just stop there. There would be too much pressure to add any additional water to the tank and the tank pressure would level out since there is no more water being added.

I also believe the purpose of the check valve is to keep any of the black water from backing up into your hose when the water is turned off.

I'm not sure if this makes any sense to any of you, but somehow it does to me!
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Old 04-19-2011, 09:17 PM   #9
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I think that the pressure from the hose would be greater than any built up pressure in the tank allowing the tank to continue filling and potentially over filling.
I would also think that if the pressure in the tank did somehow happen to build up to point that it equaled the pressure from the hose that everything would just stop there. There would be too much pressure to add any additional water to the tank and the tank pressure would level out since there is no more water being added.

I also believe the purpose of the check valve is to keep any of the black water from backing up into your hose when the water is turned off.

I'm not sure if this makes any sense to any of you, but somehow it does to me!
Ok Gary and Lou, I'll by both your explanations.
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Old 04-28-2011, 04:01 PM   #10
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It means that you should have the black drain valve open and then use the tank clusters and then use it because if you don't the tank will explode
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Old 04-29-2011, 12:19 PM   #11
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Some friends of ours used their 5th wheel as a guest house to stay in while their house was being repaired due to a broken pipe.
They have a nice pad and full hookups at their ranch.
They had the habit of leaving the black tank rinse hose connected all of the time.
They has some construction workers at their home and one of them disconnected the hose to use it else where.
When he was done he reconnected it and turned it on.
He must have thought it was the fresh water hose.
It was a horrible mess.
You cannot imagine the red tape and paper work they had to go through.
I was surprised that it was not totaled.
It was hauled away and repaired.

I disconnect mine now each and every time.

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Old 04-29-2011, 12:59 PM   #12
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Bill, An excellent lesson story.

Too many jokers around who would think that was hilarious. Like running your landing gear out with the rear stabs down buckling them; or pulling the 5th wheel disconnect lever while you are in having lunch.

Anything you can do to limit potential disasters is a good idea.
Paranoia is not unwarranted if they really ARE out to get you.
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