You need to remove the airbox, and the starter cover, to get to it.
It is located at the right-rear corner of the crankcase, on top, by the starter motor.

click for really large
You have to remove the two socket-head screws on either side of it, and then pull off the lid.
Or maybe you just stuff the pot-scrubber material down the hole after removing the rubber hose?
Bob Roller will have the answer to that.
If you remove the cover, there is a good chance you will need to replace the paper gasket, because you might tear it in the removal.