The only downside with that grey water valve conversion cap is that you have to carry along a hose for non-potable water use.
Our 50 foot hose and two 25 foot hoses are potable water rated and kept for that use so as to have the ability fill our FW tank from up to 100 feet away. Three hoses along is enough.
We prefer to carry grey water around with a small 3-gallon bucket ... although there might be (very) rare occasions where running grey water through a hose might be convenient ... if you have the room for a non-potable hose.
