There are three possible 1/8 pipe ports on the flow divider. Two are in the body and labeled inlet and gauge. The inlet's use is obvious. The gauge port is used for a metered pressure type fuel flow gauge as it connects to metered nozzle pressure. This port is not used and should be plugged if using transducer type fuel flow indicating gauges as most experimental aircraft use. The third possibility is in the cover(the top part held on by 4 screws) and it is not labeled but is a vent. It may be just a boss with a small hole in it or it may be an actual 1/8 pipe port with a small hole at the bottom of the port bore. This port should never be plugged or blocked, but always vented to atmosphere. Either left open to the nacelle or hooked to an OBD line. And btw that vent port if left open to the nacelle, should not face the front of the aircraft but either sideways or aft.
Really old flow dividers had the vent hole in the center of the cover facing up or down depending on the mounting direction of the flow divider and there was no boss or threaded port, just a small hole in the middle of the cover.
Good Luck,
Mahlon