I have recently acquired an OS FS 120 4 stroke w/ pump. On the face of the pump are three fittings. The fittings labeled IN and OUT are no-brainers, but I am not sure what the 3rd one is for. I think it is labeled D (not sure), but what is it's pupose, and does it need to be plugged, vented, or what? I have looked on the OS webpage, but I cannot find a manual for this particular engine. I did find out that it has a shorter prop shaft than the current OS 120 4 strokes, so if you are planning on using Tru-Turn or similar spinners, their normal adapter bolts will not work. If any one knows this information, please let me know. Thanks, Andy