fuel rails after they have been isolated from the filter and the return to the tank - B4 starting the engine. Prevents possible fuel hydro lock and gas in the oil and a bunch of wasted time.
Note if you use a compressor air pump to pressureize the fuel rails have a shut off valve on the compressor output side so it can be shut off when pressureized to prevent backflow of air theu the air compressure rings which could easily be diagnosed as a fuel leak.