close or open bottle
Unless you are taking bottle in and out of car all the time, it should be hooked up to all your hoses...
So even if you left it open, the most dirt that could get in there would have to travel thru the solenoid, then up the line, thru the filter if you have one, then into the bottle.
I am thinking with no juice, which ever way makes you happy will be the way to have it.
IMO.. keep it closed.

