Water fuel separator issues

Good afternoon
I am having this issue with my glass water fuel separator so I wanted to ask you guys first before I take it to the shop it’s a Frieghtliner Coronado with 3406E I have changed the filter in the glass twice in like 300 miles whenever I drain it out and what comes out of it is diesel not water it immediately starts filling back up all the way to the top so I thought it was the filter so I changed it and still having the same issue once I start the truck it goes back up all the way I checked the hoses any fuel leaking I found nothing no cracks anywhere so I was wondering if anyone has any recommendations

 

Then why is it filling up to the top of the glass once you start the truck