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Old 11-30-2019, 11:41 PM   #1
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Blacktank flush backfeeding/cross contamination?

I have a grand design 5th wheel with a black tank flush.

Previously I have always used a completely different hose for the black tank flush and a extremely careful about campground spigots to the point where I always use bleach before connecting.

During the walk through the dealer said on his unit he had made a Y with 2 separate shutoffs and only needed to turn on the correct branch of the Y to either fill the tank or flush the system and used only 1 hose.

Is this a good idea or is there a chance of cross contamination?
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Old 12-01-2019, 08:02 AM   #2
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Dealer is an idiot you don't need your black flush hooked up until you dump. Keep doing what you have been doing, it's the right way.
There is check valve and chances are nothing would happen but it is so little effort to do it correctly it isn't worth the risk.
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Old 12-01-2019, 08:30 AM   #3
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If you look at the design of the black tank flush, you will realize that more than one thing needs to fail in order to get black water backing out into the black tank flush port. I have always connected my black tank flush and city water line together when using my motorhome. In order to prevent the remotest of possibility of contamination I added a vacuum breaker/backflow preventer, https://www.lowes.com/pd/AMERICAN-VA...BoCrbkQAvD_BwE, after the Y connection to attach the black tank flush line to that so I have a redundant measure of protection.
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Old 12-01-2019, 09:38 AM   #4
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Bacteria are microscopic and will not necessarily stop just because they encounter a vacuum breaker. Think about it. How much time are you saving? What are you willing to risk to save that amount of time?
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Old 12-01-2019, 09:44 AM   #5
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i use the y as well i am not worried. i use this order pressure regulator, to y one side filter to fresh water hose to inlet other side black hose to black tank flush inlet
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Old 12-01-2019, 09:54 AM   #6
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City Water Inlet has a check valve so when using the on-board pump water doesn't backflow out inlet.


Black Tank Flush inlet does NOT have a check valve so any water in the line up to the anti-siphon device WILL flow back
Anti-siphon device is typically 2' above top of black tank
Black Tank would have to be filled ----so overfilled that contents go up vent line in order to force anything back thru spray nozzle/up and thru anti-siphon device and then back down and into hose.


Cross contaimination is Possible..........highly unlikely

Tank full enough will probably force contents out thru toilet
Anti-siphon will probably just leak inside sink cabinet
Water supply would have to be completely depressurized


Possible not not very probable





Personally I only connect flush hose when actually flushing tank
I would be MORE concerned with someone turning it on when I was not there or aware they did it........so why leave the hose connected when not actually flushing?
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Old 12-01-2019, 10:16 AM   #7
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Even with an air gap between the water source and the tank there will always be a potential for cross contamination. What each of us has to do is determine the risk, what our individual tolerances are and who to minimize the same.

Personally I would rather not have a permanent connection between the potable water and the contaminated waste side of the coach plumbing. Anything man made can and will fail and if installed on a RV will fail sooner than you might expect. Easy enough to connect a hose when the tank needs to be cleaned.
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Old 12-01-2019, 10:51 AM   #8
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I use a Y when connecting to the city water spigot. Mainly because I use one of the new black flex hoses. Issue with the flex hose is they create a lot of back pressure and when trying to disconnect it takes forever for the water pressure to reduce enough to un-screw it. Water sprays for ever. With the Y I can use one side of it to relieve the pressure. I also hookup my black tank rinse hose to the other end but don't screw it into the black tank rinse on the trailer until I'm ready to rinse out the tank. I also use a back flow on that hose.
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Old 12-01-2019, 12:01 PM   #9
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It makes sense to me, never use the fresh water hose on the black tank flush. I use a regular garden hose and never they other hose. Why would you ever take a chance of contamination. Especially when it is easy to avoid that risk.
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Old 12-03-2019, 12:24 PM   #10
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I dont see any advantage to using a Y.
If it saves you seconds of hose hookup are you really that tight for time?
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Old 12-03-2019, 04:49 PM   #11
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Blacktank flush backfeeding/cross contamination?

Quote:
Originally Posted by Old-Biscuit View Post
City Water Inlet has a check valve so when using the on-board pump water doesn't backflow out inlet.





Black Tank Flush inlet does NOT have a check valve so any water in the line up to the anti-siphon device WILL flow back

Anti-siphon device is typically 2' above top of black tank

Black Tank would have to be filled ----so overfilled that contents go up vent line in order to force anything back thru spray nozzle/up and thru anti-siphon device and then back down and into hose.





Cross contaimination is Possible..........highly unlikely



Tank full enough will probably force contents out thru toilet

Anti-siphon will probably just leak inside sink cabinet

Water supply would have to be completely depressurized





Possible not not very probable

Personally I only connect flush hose when actually flushing tank

I would be MORE concerned with someone turning it on when I was not there or aware they did it........so why leave the hose connected when .............




A lot of black tank flushes have a back flow preventers, my current wildcat 5th wheel has it and my previous camper 27hfs had it.
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Old 12-03-2019, 05:32 PM   #12
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If you're so concerned with cross contamination that things like this actually make you worry, then you shouldn't be in an RV. There is absolutely no way to keep the systems totally separate without using new every time you connect something.

I pull in to a newly setup RV site and hook up my white potable water hose to the newly installed spigot and go on about my business. Eventually, I'll need flush my black tank, so I remove my new white potable water hose from the new spigot and attach my non-potable old fashioned rubber garden hose to the spigot and my black tank flush. Oh no! I just contaminated the new garden hose with poop bacteria! But that's okay, the water was only flowing one way so it didn't contaminate the spigot. When I'm done flushing, I put special black tank flush hose caps on the ends of the hose so that nothing leaks out. Now I put that hose back in storage and continue using the RV cuz that's where I live.

A few days or weeks go by, and that pesky black tank is full again. Time for another flush. I get out the capped off black tank hose and suddenly realize that the whole hose is contaminated with poop bacteria. It's been wet all this time and the bacteria have populated the whole hose! That's okay though, because it's just used for the black tank flush. I take off the white potable water hose off the new uncontaminated spigot once again and put the black tank hose on it, contaminating the spigot. Then I do my thing, and cap the hose once again to be sure that I don't cross contaminate anything. Then I take my white potable water hose that's never been contaminated, and hook it up to the freshly contaminated spigot. Run water through that hose and I've now contaminated my potable water hose and the entire fresh water system in my RV!

Sure, you can bleach the spigot, but even bleach isn't 100% effective. You're never going to kill all the bacteria. Would you lick the spigot at every campground you connect your water hose to? Why not? That's basically what you're doing every time you use the water there to cook or clean or just drink. You can even add fancy adapters and extra connections, but as long as you're using a single spigot for all your water needs, it's going to get contaminated. There is absolutely no way around it.

The best thing to do is simply stop worrying about it. The human immune system is set up to handle all that stuff. It's truly a wonderful thing, but it needs to be taught how to do its job. That's why babies put everything in their mouths. They are teaching their immune system about which bacteria are normal and not a problem, as well as which ones are a problem. If they never experience normal bacteria as a baby, their body doesn't learn that it's okay, so when they experience it later in life, they have allergic reactions and can't handle it. People need to be exposed to some bugs. It's healthy for us. Raising babies in sterile environments does them far more harm than good. Sure, they might get sick fewer times in infancy, but they'll have a much worse time in adulthood.

Don't misunderstand! I'm not saying you should be as dirty and nasty as possible. I'm just saying that you shouldn't worry so much about being perfectly sterile either. That cookie that fell on the floor is fine even if you've walked on that floor with your shoes on. The 5 second rule has its merit. I wouldn't eat spaghetti that fell on the floor, but a cookie or a grape from the floor once in a while is okay.
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Old 12-05-2019, 12:11 AM   #13
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We travel with three dogs. The dogs like to sit on our couches and laps. Sometimes I let them eat dog cookies out of my bare hands. Sometimes dogs eat things we don't think they should... I grew up with dogs (and cats too) and somehow we have survived all that cross contamination. I have been "camping" much of my 76 years. I also use a "Y" fitting on the fresh water bib, I only hook the flush to it when it's time to flush tanks. I shut off the fresh water at the "Y" and I drain the black tank first, close the black valve and drain the grey, close the grey valve and then flush and dump. When finished I disconnect the flush hose after flushing it out. So far we are still alive and healthy. I think common sense has kept us that way.
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