black tank clean out

I bought a used 09 Montana mountaineer towable last year and I think the previous owners did not winterize the black tank clean out spray system. any way, when I turn on the water to the outside hook up, water comes out from under the water heater. I found this out in Yuma last year and so today when I pulled the cover behind the water heater to turn the bypass valve I looked around and saw what looked to me like a back flow device inline with the water line running to the out side connection. I didn't spend too much time worrying about it at the time but I think that is were the water is coming from. I think next spring I will have someone watch to see where the water is coming from and don't know if I can just put a nipple in line and use an out side black flow device on t he system. I have never seen such a valve such as this and I'm guessing I will have to get one from Keystone. they sure aren't in the RV parts catalogs.