Refer to the plumbing diagram and partial elementary school floor plan. If the trap of a floor drain is at HH is 6` from the vent, the minimum diameter of the horizontal drain line HHGG is ____.

Refer to the plumbing diagram and partial elementary school floor plan. If the trap of a floor drain is at HH is 6` from the vent, the minimum diameter of the horizontal drain line HHGG is ____.