A metering tap comprising a housing and a rotatable valve disposed within said housing, said housing having an inlet and an outlet, the housing and the rotatable valve forming a chamber of a preselected volume wherein in a priming condition the rotatable valve is oriented whereby the inlet is open and the outlet is closed, wherein in an intermediate condition the rotatable valve is oriented whereby the inlet is closed and the outlet is closed, and wherein in a dispensing condition the rotatable valve is oriented whereby the inlet is closed and the outlet is open.