Help me diagnose last couple bugs on the swap.

I tested all the injectors and cleaned them out, so I believe they are good.

I'm assuming there is some sort of check valve on the supply side? Google is saying there may be one in the pump?
The regulator would also have to seal, correct?
How do I test which of these items is bad?

Edit:
Just read the FSM, which has a great explanation of the system. There is a ball check valve on the outlet of the pump. The pressure regulator is supposed to seal the return side.

Tomorrow I'm going to pinch the hose to see which side is leaking. My hunch is that it is the pump. Will update later.