Fuel pump parked up hill

Please tell me more about the constant circulating system.

After my last post, I went to measure the pressure put out by my mechanical fuel pump.
I was working blind and thought I knew what was under there. I twisted a fitting right off the pump. Did not think it was a good idea to try and weld it back together :).
I ordered a generic fuel pump that had a filter before the pump. I mounted it a few inches (about 6 ) above the fuel sending unit. Bolted it to the underside of the trunk.
Beside the filter that came with it, I put in a new filter in the same position and the one I had.
The fuel lines were empty and it took about .5 seconds for the gas to splash in the 2nd fuel pump. Wow that was quick.

Without thinking I pulled her out of the garage a left her on the driveway (facing uphill) without giving it a 2nd thought.
An hour or two later, I realized what I did and dreaded trying to start the car. Started like it was brand new factory fresh.


second fuel pump?? why is the mechanical one still on the car, it has to be removed