The High-Pressure fuel pump in the engine bay (as opposed to the in-tank sender fuel pump) has to be bled first, if I remember correctly. -Failure to do so correctly results in the stored high-pressure fuel being sprayed as a fine (and extremely combustible) fuel-air mist inside the engine bay. -If the engine is hot, it's not a safe place to be, and if there's any spark or naked flame around... it doesn't end well!
I know a geezer who got fuel sprayed in his face, dropped the spanner which was in his hand, it made a spark, and "woof"...
With a "how-to" I know that it can be done, but you DO need to know which steps to be extremely dilligent and careful over.
Keith