Just did another one this week, always seems to be a 420 never a 560, weird.
The pipe (the rubber attaches to) is part of a banjo fitting straight down behind the linkages at the center back of the motor. It is so far back that the area can be seen with the aircleaner still attached. I forget what is fed by that banzo fitting, probably all the inside vacuum units (AC). If you follow the brake booster vacuum line it will take you within two inches.
Bosch Master, ASE Master, L1
33 years MB technician