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They are those trashcan looking things with a square green light on the front of it, above a line of text, "PNEUMO", in white. They're used to send items quickly over large distance via air chutes. If you meant where it was, it is beside the door a Brute Splicer was trying to get into at Little Eden Plaza. Near a Butterfly Memorial and across from a Health Station. Sorry about the poor directions, I forgot where it was :P