I'm getting a new battery for my '99 E300. Everyone said to get a battery that has provision for the 'vent tube' etc. The problem is that in removing my original battery, I dont see any vent tube of any sort. I'm wondering what it is, and what I need to hook up upon installation of my new battery? Thanks!

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2004 Ram 2500 Cummins HO
2000 Jetta TDI
1999 E300 (sold)