After I am done spraying, I pour a little of the reducer, or thinner i used in the paint. I take a small natural bristle brush, and clean the inside of the cup, to get the paint off the inside of the cup. Pull the trigger on the gun, let some of the reducer run out. Dump the cup, if necessary.
Pour more reducer in the cup, and brush the inside of the cup again. Connect the gun to air, and spray the second batch of reducer through the gun. While spraying, take a rag and cover the tip of the gun, and seal the tip enough to "back flush" thinner and paint backwards back into the cup. Remove the rag from the tip, and spray normally. Do this several times. The back and forward motion of the reducer and thinner helps to dislodge any paint left in the gun.
I will then take the cup off, and wipe out the interior, and exterior of the cup with paper towels, and thinner or reducer, or general purpose solvent. Sometimes I use a filter in the bottom of the cup, in the throat of the gun. Pull it out, and brush it off with solvent, and blow compressed air backward through it. Brush the inside of the throat of the gun, where the cup attaches.
Put the cup back on the gun. Pour a little more solvent in the gun, and hook up air, and spray again, again using a clean rag, or paper towel to cover the air cap, back flushing the gun again. If you see ANY trace of the color or primer you were spraying, Repeat above steps again.
If you are seeing no trace of color in the cup of the gun, and no trace of color on the rag, or paper towel, use the damp paper towel to wipe off the exterior parts of the gun. Use the brush to reach small areas you cannot wipe with a rag.