This is an old idea but still a very clever way to quickly swap over gas bottles. The cock is a 3 way tee with a tap to divert the flow from either bottle to the van. Don't forget you do need to have a gas fitter to install this modification. Apart from the convenience of not having to fiddle with hoses another huge advantage is both cylinders are sealed so you don't get dirt in the fittings.

Bob Eustace