This fitting should always be mounted in the vertical upright position (shown below). In this condition, air flow is permitted to move through the unit in both directions (in and out).
This block is machined with one 12AN ORB port and three 10AN ORB ports. There are enough fittings to make a 3 into 1 adapter. However, it can be converted to 2 into 1 if the 10AN ORB plug is used as shown below.