IIRC, it's right below the bullet part. It's simply a hole on the leading edge of the unit.
I'd try blowing the line clear. Fromthe speedo side use a bicycle pump and try to blow the line clear ( detach from teh bullet first )
Also, if it was left all winter, something may have crawled up there. Blow out from the line, at the bullet too.
The lakes I'm in have a bit of algae that seem to pug it. Also, sand from beaching always gotup in there.