91 fuel rail return test?

I can't find a description of the fuel rail return or how to test them in the FSMs (checked engine and emissions both). I had a bad pump, showing okay pressure at idle but would collapse to 0psi as soon as the engine was killed, also would bog on acceleration sometimes, both pointed to bad check valve. I had a backup pump (long story) that seemed to have functional check valve on my bench test with the funnel, and no more bogging, but pressure still drops very fast. Leaky return?

Guess I could clamp the return and see how fast pressure drops through supply