Festo quick fittings
Be careful with festo quick fittings in the suction side of you fuel system, especially between your last tank / uat and the pump.
They can, and they will leak.
I've had it happen: there was a tiny bit of air accumulating in my fuel filter just before the pump. The festo vacuum filter lets you monitor that.
No visible air leak could be seen, but the air bubble in the filter grew ever so slightly after every flight.
After converting to solid connections, no more air in the fuel filter.