lift pump / check valve / fuel drainback issue

Have read dozens of posts about lift pump / FSS / injector pump issues and have learned a lot! Thanks!

I have a 91 F 250. Lift pump delivers plenty of fuel. Once the truck cranks it runs great. No leaks at any of the fuel lines from the injector pump to the injectors.

I believe I'm having a check valve issue. After sitting overnight, the truck won't start. Fuel filter has plenty of fuel, and there will be plenty of fuel in the line between the filter and the injector pump.

The line between the lift pump and the filter will be completely empty, indicating that all the fuel has drained out of it.

This doesn't happen every time the truck is left overnight. Sometimes the line stays filled with fuel, and the truck fires and runs beautifully.

Is this a check valve issue?

Where is this check valve located?

Do I have to change the lift pump (which is delivering plenty of fuel) in order to fix this issue?

Is there a way to try and clean the check valve to see if there's a piece of something in it causing it to intermittently hang open?

Also considering bypassing it entirely and putting in a DC fuel pump w/ check valve.

Thanks in advance for the help.