This device has Two functions.

First function is to draw the air out of the ink line during the priming process. You simply insert the ink needle into the tiny hole on the end of the rubber fitting on the prime gun and then turn the prime gun on and the pump will draw the air out of the line.

Second function is to unclog the print heads. Simply press the rubber fitting onto the bottom of the print head so that you have an air tight seal... and then turn the prime gun and the suction from the pump will draw ink through the jets of the print head. It is suggested to only turn the pump on for just a few short seconds... and repeat this roughly 3 times.