I did just try and suck ink out of the priming port (= side exit valve port). I had to remove the plastic plug to get the syringe tip in, and there is ink down the hole. The air vent plug was out, the fill port plug was in. No ink came up into the syringe although it was sucking hard. I tried priming with the priming tip on the syringe and got ink into the syringe with no effort.
If I can offer a suggestion, adding a few labeled pictures of a cartridge to the printed instructions would be helpful. The various ports could be labeled, and "top", "front" and "back". I note in my message above I said the exit valve was on the back of the cartridge and just noticed that the instructions say the ink fill hole is on the back. A picture of the priming tips would be helpful, too, or possibly just a label on the plastic bag they come in.