most guys use a redbull can. you can easily make one out of PVC as well. (pipe + 2 caps, drill a hole and run your tubes)
i think it mentions something int he rule book about having a bellypan and whether or not you need one.
some guys run both options.
here you go
Route all vent, breather, or overflow tubes coming from the engine, transmission, or radiator into either a heatresistant
catch can of at least 350cc capacity, or the air box, which must be sealed to prevent fluid leakage. The
airbox may remain unsealed provided the bike is fitted with a closed belly pan.