Basically Fred, an oil trap is a can with an inlet and an outlet. The exhaust steam and crud goes in and the oil drops out allowing “Clean” steam to exit and up a chimney. Make sure the inlet from the engine points downwards so you don’t get a “Blow through” effect. When he designed it, I don’t think Basil?? thought about “The Enviroment”, he was just trying to get people re-interested in steam propulsion.
Regards Ian.