[Carl n Susan]

Sorry, but I am positive the RV Tech didn't know what he was talking about. That is a anti-siphon back-flow device for the black tank flush system. The washer liners are color coded Red/Blue as are all the normal Hot/Cold water lines. The only white water lines in a Montana are for the black tank flush lines. You should ensure you add an anti-siphon device to the black flush hose to ensure the black tanks doesn't back flow ( a very unlikely event but possible).