Anybody know what this is?

[Vision]

Can't figure out what this is, why it's capped, and it appears to have fluid in it. I don't see it mentioned in the manual.

Is it an oil overflow tube? Should it be drained periodically?

[Stig / Major Tom]

Well, it is connected to your airfilter box, and can collect oil mist and other mysterious  (to me) and smelly liquids.
Anyway, Yes drain it periodically.
And no, never overfill with engine oil - there is no healthy way for your scooter to get rid of it.
Stig

[Vision]

Thanks. Strange it's not mentioned in the manual.

[CROSSBOLT]

Thanks. Strange it's not mentioned in the manual.

Many things are not mentioned in either owner's or service manuals. Many things that are mentioned are either incomplete, incorrect or incomrehensible.

[Neil955i]

Didn't someone on here refer to it as a "burp tube"? 

[Iahawk]

'puke tube'

[Neil955i]

'puke tube'

Thanks Hawk, that was it.