quickdrawmacgraw

Hi all, Steve here new member and i've just got myself 2005 yz 125 but not ridden it as yet apart from the test ride which went ok but after i start and let it run for a few minutes in my garage i get one drop of oil under the bike from the black rubber breather tube coming from the front of the engine. Now seeing as i'm not mechanically minded when it comes to bikes should i be worried about this or is it some sort of exhaust port for excess two stroke oil or something. Any info gratefully recieved. Thanks Steve.