Hi Mate,
They are the over flow pipes. You can tee them together and connect them to the fuel return line to the tank or just leave them as is.
I chose to leave them as is as I didn't want heaps of hoses everywhere. They are also made from soft rubber to so getting a good seal may be a PITA.
In all the readups I have read everyone leaves them as is.
What carbs on what engine are you using?
Cheers,
Matt