Are both the bottles in the outside locker connected? If so the only thing I can guess of it being is an electric valve that switches from either one bottle to another or connects both together when one bottle runs out, to me it looks to be retro fitted and not a standard fitment.
As Neil says they do recommend that gas hoses are changed very regularly.
However what I do with mine is I check them with soapy water annually, if there is a leak it bubbles up. I know that others would not like doing it this way but it works for me and is not meant as a recommendation to others.