13 Prostar no start after sitting 2 days..

My truck is having problems starting after sitting for two days.. After two days the fuel filter (water separator) is empty and I usually have to fill it and prime the system.. The truck cranks and run fine afterwards.. Only gives me trouble during 36hr resets..

 

Is the check valve inside the Davco or outside?

 

Would you happen to know what size the nut head is on the inlet side? I don’t think I own a socket thats big enough to get it off..

 

It was the check valve and the socket size is (1 1/4”) tighten to 60ft-lbs. Hopes this helps someone in the future..