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Old 09-22-2015, 10:43 PM   #11
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Originally Posted by OldCoot View Post
How do you get pressure in the tank with it vented thru the roof?
If they overfill the tank to the point of a gyser out of the vent and turn the water off I bet something would flow backwards. All this being said I would not tie everything together.
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Old 09-22-2015, 10:45 PM   #12
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Originally Posted by NV245 View Post
Lemme see, back flow from black tank, full tank to flusher, pressure in tank, anti backflow device don't work... and da second backflow preventer in Phil's illustration don't work either. Yep, definitely a big no-no, ya got every probability of getting poop in yer fresh water


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I'm not going to do the mod but the black tank is vented and there is this big hole coming thru the floor called a toilet. If the black tank is installed correctly there is no way for backflow to occur (my opinion). This is a typical rv cleanout I believe:
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Old 09-22-2015, 11:04 PM   #13
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Originally Posted by NV245 View Post
Lemme see, back flow from black tank, Please explain??

full tank to flusher, Hydrostatic pressure does not work sideways.

pressure in tank, again please explain how pressure gets in a vented tank??

anti backflow device don't work...how would it flow back?

and da second backflow preventer in Phil's illustration don't work either. It's a valve, not a flowback preventer, close it, it works.



Yep, definitely a big no-no, ya got every probability of getting poop in yer fresh water.


I disagree, I have a similar set up made of short sections of hose with valves in strategic places. Mine WORKS!! I have no poop in my fresh water.
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Old 09-22-2015, 11:43 PM   #14
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I don't have a dog in this fight mostly because it's just not good poker. The fear is a vacuum in the fresh system and the path of least resistance being a connection to the grey or black water. I cannot see any plumber person approve of any connection between fresh and waste water....then how do you flush? I dunno. Just doesn't look good to permanently tie fresh to sewer.
It wouldn't take much black to contaminate the fresh....and you wouldn't know it till "you" started filling the black.


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Old 09-23-2015, 12:09 AM   #15
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I do know that when I turn off water to my black flush, it has pressure in the hose and pushes water back out. May not be Blackwater but it is water.
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Old 09-23-2015, 06:58 AM   #16
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I do know that when I turn off water to my black flush, it has pressure in the hose and pushes water back out. May not be Blackwater but it is water.
Yes, it's residual water from the input side of your backflow preventer that is in the tubing leading to the shut off plunger in the preventer. It's fresh water. All the water on the other side of the plunger has drained into the black tank. The preventer is mounted probably 3 to 5 feet above floor level and that distance will determine how much fresh water drains back out of the pressurized side tubing. It's just gravity flow and even without the preventer and the way the cleanout is routed I doubt there could be any water from the black tank getting back to the external input port. I'm outa here.
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Old 09-23-2015, 07:16 AM   #17
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Just my opinion, but knowing that there are organisms in the black tank that can kill you (literally), I personally will take the extra minute to connect my black tank flush separately. I see no reason that you can't connect the two fresh water intakes together, but since I don't dry camp I usually fill my fresh water tank halfway at the beginning of the season (after cleaning) and leave that supply in there.



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Old 09-23-2015, 09:17 AM   #18
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Yes, it's residual water from the input side of your backflow preventer that is in the tubing leading to the shut off plunger in the preventer. It's fresh water. All the water on the other side of the plunger has drained into the black tank. The preventer is mounted probably 3 to 5 feet above floor level and that distance will determine how much fresh water drains back out of the pressurized side tubing. It's just gravity flow and even without the preventer and the way the cleanout is routed I doubt there could be any water from the black tank getting back to the external input port. I'm outa here.
Probably. I still don't want that water that has been close to my BT feeding back into my fresh water hose.

The instructions for the flusher does say to disconnect water hose and let the pressure push the water back out of it.
It also says to not use a potable hose on the BT flush.
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Old 09-23-2015, 10:16 AM   #19
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Hi Phil,

I connected the two fresh water feeds together but not the black. I have been thinking of getting a pocket hose for the black flush. To follow is a picture. Poor as I still do not have my coach back to take a better one.
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Old 09-23-2015, 10:24 AM   #20
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Silver I like that. I don't really know if I would hook the three together. I was initially disgusted by it in my friends Newmar but I love the ease of use. I don't trust a backflow that much when that's about the only thing keeping me from drinking Poo water. I might work up a system to fill without having to change the hose but the BT and fresh water will remain separate. I mostly wanted your opinion and I thank you for that.
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