sani flush black water holding tank

I have a "Y" on the end of the fresh water hose. It has shut off valves. I have a short hose with a quick disconnect from one side of the "Y" to the flush connection. The other side goes to the fresh water connection. The flush system also has an anti-siphon valve. When I need to dump and flush, I attach the short hose and turn that side on... AFTER I turn the fresh water side off. After flushing, I turn the flush side off and disconnect that hose. I then turn the fresh water supply back on. If I am at a dump station, I use a separate hose, not my fresh water hose. I store everything in appropriately designated areas. I always hook up fresh water before any sewer water connections and I wear rubber gloves for waste water handling. I'm very careful not to contaminate fresh water. We have two filters, but we still don't drink water from the tank.... ever. It is for cooking and hygiene only.

With a 25' hose priced less than $12, why would you want to.:h.....Dennis

I have a device that I hook to camp water, so I can have fresh water hose and gray hose. At gray hose I have an extra back flow valve as well as on and off water valve. Course there is another back water flow valve at flush area.

I don't see what can happen. There is a check valve and the inlet is well above the tank. Furthermore, the tank would have to be full and pressurized somehow (how?) to the point that it overcomes the pressure of the water hose you have hooked up to it. Then the brass check valve would have to somehow fail at the same time. (and if the tank pressurized it would split long before it hit 30~40 psi).
All this happening while water at real pressure is pushing against it.

One more thing to consider, if you think the tank can pressurize enough to flow back into the hose somehow then the contamination wouldn't stop there. It would include the hose bib and CG plumbing.
At some point you still have to connect city water to it.

Absolutely NOT. Very unsafe and downright dangerous for your health. That could spread hepatitis and a whole range of other nasty diseases if you do it on the black and then use it again on the fresh water. Go buy a new fresh water hose and use your existing for the black rinse. Wrap each end of the old hose with widely spaced turns of black electrical tape to indicate it being for black and grey use.

I use a separate hose. Although the risk is pretty low why it's one I would prefer not to take. I like multitasking items in the coach but the white hose is only used for one thing, potable water.

I will add this, if you do use a separate hose please do your self a favor and store it with the sewer things not your fresh water hoses.

Short and simple NO HOW NO WAY!!!

I use a el cheapo garden hose

I would not use the same hose for the flush and for drinking water. No way. Even if there is a check valve, it can leak or fail.