Neil is completely right. Keeping the system primed can ensure speedy uptake. Regarding the non return check valve, it’s worth considering the volume of water held in the pipe from the bilge to let’s say a manual whale type pump (often located meters away!
A 1.5 inch pipe will hold 1.14 litres per meter! Scale that up.
It can be quite annoying when those last few litres just flow back down into the bilge when air enters the system or you stop manually pumping upon hearing the last gurgle.