sani flush black water holding tank

I'm sure you could but I use a separate hose, but I've wondered the same thing. What stops me is the sewer hose is usually nearby or attached to the drain valve. I usually have the fresh water hose disconnected and stored separate when dumping.

rv dealers have a grey hose used for the flushing of black tanks. they come in various lengths. I sure wouldn't take the chance of using my fresh water hose to hook up to a black tank with or without a back flow device.

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.

I use a el cheapo garden hose

Short and simple NO HOW NO WAY!!!

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.

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.

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 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.

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.