Speed Twin -what's This Tube Then?

If it’s attached to the airbox then I’d say it’s to catch any oil that gathers from the breather system. It’s clear to show when it needs emptying/cleaning? Just an educated guess.

 

It’s a fly trap

 

It clearly works then.
Didn’t we have a thread recently about flies and what to do with them.

 

Its so you can tell if your flies are low.