OK, I know there is supposedly no such thing as a stupid question, but I fear this one may come very close. I will know when the replies are posted. Yet, it must be asked, before I can proceed with the installation of my VDO boost gauge:

On the rear of the gauge are the two mounting studs, the light, and the brass nipple to which the plastic line is run. When I remove all the fittings from the nipple and look at it, there appears to be a brass plug where I expected to find a hole. I have looked at this thing closely wondering if it is some sort of filter or moving component; it appears to be neither. I gently scratched it to see if it was metal rather than some fiber insert; it is metal. For all the world, it looks like a brass plug … and it looks to be airtight. I can't see how the vacuum or boost pressures can get to the gauge sensor to be displayed by the needle.

And, yes, I did check the archives, but didn't see anything addressing this issue.

So, c'mon, guys. Is there some little secret you (and IPD) are not telling me? Open to any and all comments and suggestions.
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Dave in Virginia