I was just dealing with that as I was hooking up the Factory lines that I refurbished. I swore that it was clogged but then I got to cleaning it out and it rattled.. then I figured out it was a check valve... For the life of me I've seen one of those around my shop and I searched and I searched and I searched a couple days ago... The reason I noticed is because about an hour ago I stumbled upon it when I wasn't looking for it just like I knew I would one day...