this is the corse breather for 748/9x6 built onto the seat undertray
it’s well over 3 litres (the stock ‘splitter’ on a Monster is a bit under 1 litre) it essentially fills the seat hump.
It breathes through a block on the crankcase with no reed valve (restriction).
The outlet pipe then runs to the airbox, where a reed valve block lives to stop air being sucked back in, you can see that on the left, just behind the rear throttle body in pic.2