Abstract: A separator for oil well production fluids including oil, water and gases in which the separator includes a water siphon system having a vertically adjustable spill point for the discharge of water to a collection or disposal area for changing the interface level between the water in the bottom of the separator tank and the oil on top of the water in the separator tank. The separator is primarily constructed of a non-corrosive, non-conductive, high impact plastic with the siphon system and standpipe being positioned internally of the separator tank to reduce damage caused by high winds damaging such components by blowing down the separator which may have been weakened by corrosion with this arrangement also reducing the possibility of water in the siphon and standpipe being frozen which can occur when these components are oriented externally of the tank.