Fuelrail ? 2000 gts

I cleaned injectors installed o rings and filters,Thought the reason my fuel rail empties after shut down possibly a leaky injector.What I want to know is the donut on bottom of fuel rail ,is it just a port ,check valve.or regulator.I know theres a regulator built in the fuel pump.Maybe someone had this problem ,takes several cranks to start then runs crapy for 40 seconds while purging air.I have been using a push button to turn fuel pump for 4 seconds ,it starts right up but still have 40 second crapy purg..My 2000 gts runs great just getting the last few bugs out.