Of course copper pipe might last longer, but white metal or water pipe would be just as good. The size of pipe would depend upon your boiler connections. The boiler is then prepared to run and pressure is built up to about 150 lbs. The steam goes in at the bottom and passes through and goes out the top, filled with the oil. While steam will mix with the oil, water will not.
Water separates itself from the oil in the receiver.
However if the oil is heavier than water, the top valve is opened and the water is forced out as it rises to the top and the oil can be let out from the bottom easily. In this article I have not gone into details on extracting oils from any particular plant or wood.