How do you check for fuel system leaks?

I have a serious leak in my fuel system somewhere. I cannot see gas physically leaking and it does not have gas in the oil. I am pretty sure the fpr is bad, but how do you check for leaking injectors? Why do they leak, extra o-ring not letting the injector seat in the fuel rail, bad o-ring? Any help is appreciated.

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88GT stock shortblock, ported GT-40 iron heads, ported Edlebrock Performer intake, 24# inj, Pro-M 75mm Bullet MAM, 3.73, hurst short throw, F-303, electric fan, alum rad, FMS HD clutch, R134a ac conversion, 70mm TB , and some other stuff I probably forgot, best run so far on ET streets is 13.02@106 with a 1.87 60ft (Full body weight GT, full tank of gas, and sway bars connected, gonna disconnect sway bars and dip into the twelves).