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Old 07-28-2009, 11:10 AM   #71
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I have a back flow preventer in the flush system. I also disconnect the hose from the trailer first after turning the water off. This prevents any back-flow that might occur from getting in the hose. But one thing to remember is that the inlet for the tank flush is several feet away from the actual black tank. It is reasonable that the water doesn't flow through the whole system to get inside the hose and work its way back to the faucet through the length of the hose in the second or two that it takes to get from the faucet to the hose connection to the trailer. Plus, the water in the hose is under pressure still and keeps the water away from the faucet.
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Old 07-28-2009, 04:52 PM   #72
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Originally Posted by eubank View Post
Good question. Here I do a visual inspection of the device, making sure that the plastic one-way valve on the inside is not broken or stuck. Then I can hook one up to any faucet, turn the water on, turn it back off, and watch. A good backflow preventer will squirt water out the sides as the faucet tries to suck water back down; a bad one won't.


Lynn
Lynn,

Appreciate your comments but it wasn't a question.

There are well defined requirements for different sanitary applications and risk levels. The difference between a testable and a non-testable device is well defined. Many jurisdictions only allow 'testable' backflow prevention devices in a medium and high risk application.

The hose bib antisiphon devices and check valves are rated as non-testable devices, which is why some places don't allow them as backflow preventers for flushing sewage tanks.

And since they are suitable in low risk situations, you can still buy them at your local hardware store. It's up to you, and your neighbors, to know when they can be used (like at the dump station) and when you shouldn't use them.

Otherwise, it's a crap shoot. Nothing worse then a good case of gastroenteritis when you're on a camping trip.
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Old 07-28-2009, 04:56 PM   #73
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Originally Posted by Minnie's Mate View Post
I have a back flow preventer in the flush system. I also disconnect the hose from the trailer first after turning the water off. This prevents any back-flow that might occur from getting in the hose. But one thing to remember is that the inlet for the tank flush is several feet away from the actual black tank. It is reasonable that the water doesn't flow through the whole system to get inside the hose and work its way back to the faucet through the length of the hose in the second or two that it takes to get from the faucet to the hose connection to the trailer. Plus, the water in the hose is under pressure still and keeps the water away from the faucet.
It is one thing to bet one's own resistance to giardia on such a setup; it is quite another to bet someone else's.

In all probability what you've described will work OK for very much of the time. However, I still wouldn't do it (personally), as I'd hate to bet on the backflow preventer having a failure rate of zero.
Also, there remains the physical connection - and the hands, even gloved hands, making one connection then the other then undoing both. The same hands are contacting all surfaces and are capable of spreading parasites. I suppose you could develop a procedure that involved two glove changes and three handwashings, but would the next guy follow it?

I'm not normally squeamish, but this makes me feel not-so-good.
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Old 07-28-2009, 04:57 PM   #74
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...
Otherwise, it's a crap shoot....
Nice touch.
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