I had the same thing with mine when i first got my Tenere.

I took the bung out of the bottom and a fair bit of watery oil came out. Well not that much but the hose was backed up by about 5cm.

It's the drain from the very bottom of the airbox and i don't know how the oil/water got in there. I have left the plug out so it can drain. As far as i can tell the plug is there just in case you go through a deep river.

I don't do that so i can't see any way water would get back up the hose.

Mike