Jeep 3.1TD Fuel draining from engine or fuel pump problem?

I have a Jeep Grand Cherokee 3.1TD 1999. The engine seems to drain of fuel while parked and can not source a leak. I have put a one way valve after the fuel engine filter but before the pump, but that doesn't help.

At the engine fuel pump, one hose goes to the engine and a second is a return hose back to the fuel tank (I think).

Question 1. Does anyone know how to test the fuel pump without dismantling the engine?

Question 2. Does anyone know if there is a tank pump on Diesel Jeep Grand Cherokees?

Any advice appreciated.