[JohnMD]

Thanks for the feedback, Bill. I plan to open it up this weekend to sanitize the water system and will measure the diameter of the tube and hole then. I am certain that the previous owners never had a solar system as they said they almost always used electric hook-ups. In fact, the battery was dead and dated March 2010 and all of the contacts were very corroded...not sure if they had ever been maintained. I am operating under the presumption that this must have been an added option for potential venting.

John