I seem to remember in an issue of model engineer a chap fitted an oil trap in the smokebox of his loco,
it worked by passing the exhaust into a circular drum via pipes entering the sides at an angle, this swirled the exhaust round and round throwing the oil to the sides ,the oil then ran down the sides and out the bottom whilst the steam exited up the chimney.
I can try and find the article if you like.
cheers
Roy