For example,
backflush SOP's:
I am not sure why this necessary but simple procedure causes so many folks to pause. A spoonful of Urnex in a blank handle; lock into a hot machine and run the pump until it goes quiet; repeat pump on/off until draining water is grunge-free. Remove handle, rinse it off and repeat without Urnex, rinsing residual cleaner from the 3-way solenoid, until water runs clear. The good barista also wipes off the grouphead, dispersion screen, gasket, etc. with a wet cloth and/or soft brush and clean water to make everything just right.
If your (Gaggia) machine spits hot water when you pressurize a blank, it'll spit hot water AND acetic acid when you backflush with Urnex. Take necessary precautions by defending yourself (and your property) from the scary hot acid grungy spray that usually dribbles neatly into the drain tray on practically every espresso machine made. Like, you know, put an old towel by the overflow tube and never stick your eyeball up close to see what's about to spurt out.
C'mon! People! We are pipe and cigar guys. A little hot acid spray won't keep us from cleaning our gear.