The plug comprises a valve seating portion having a valve opening therein and a valve head adapted to seat on the seating portion and bias means extending between the seating portion and the valve head to bias the head to the seated position on the seating portion when {HEAD ~ the separator tube} is stationary within {TAIL ~ the collection tube} 
is stationary within
The plug comprises a valve seating portion having a valve opening therein and a valve head adapted to seat on the seating portion and bias means extending between the seating portion and the valve head to bias the head to the seated position on the seating portion when { HEAD ~ the separator tube } is stationary within { TAIL ~ the collection tube }
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