Originally Posted by f1100turbo
Back flow preventers do work as you say as long as it doesn't stick "open" as the check valves commonly do on the fw inlet.
One time of that and you'll use a seperate hose. Imo
Ahh, I wasn't clear - I wholly suggest using separate hoses. One hose for my black tank flushes (either a the built-in tank flush or the product that was mentioned) and a SEPARATE set of hoses for my fresh water inlet.
However, I do hook up a wye to the hose outlet and hookup one side to my sewer hose and the other to my fresh water hose. Given the propensity for back-flow preventers to malfunction, I'm possibly cross-contaminating my fresh water hose anyway.
I'd guess the only way to properly protect against that is to disconnect my FW hose when I do my black tank flush and when I reconnect it - clean the spigot with bleach.
Given that I'm moving to quick hose disconnects. That might not be too bad to do.