Chinook RV

On my Chinook, there is the usual plastic door for the city water and where you fill the water........then on the back of the Chinook on the drivers side, there is another water fill female hose thing. Does anyone know what that one is for?

On my 2002 Concourse that rear hose fitting is to flush the black water tank

Same here, only on my '99 Concourse. The female garden hose type round fitting on the driver's side rear is connected to a black tank flush system.

By the way, if you add your Chinook's year and model to your profile (or your signature, or both), it can be helpful.