What you have is a collector for the air box drains, probably home built. It is intended to be emptied from time to time. If it is coming out of the bottom, perhaps it is missing a plug.
If it is overfull then it hasn't been emptied in a very long time or you have excessive oil in the air boxes, perhaps from using the wrong oil or a lot of idling.
Empty and clean it all up then monitor for a while.