I sold an Ammo Airviper airbrush and the customer said it didn’t work, so I got it back off him and tried it myself, it’s not working right, I’ve given it a full clean in the sonic cleaner and when I press the trigger air comes out but no liquid (water for testing) the only way I can get it to spray right is put my thumb over the cup, so it must be something to do with the air not getting to the right place, has anyone else ever had a similar issue?