To test the plug behind the fuel filter housing, compressed air in thru the inlet. You can also test the plug beside the fuel inlet seat, but be aware that high pressure air can send that plug out like a bullet! So don't have it pointed at your face when you do this!!!!
The bottom plugs are tested as shown in our book, by inverting the casting, coating them with a soap/water mix, and apply high pressure air to all 4 jet holes.....Cliff