I know we are talking different models here, but I replaced a leaky fule line on my W124 a few months ago.
My only real preparation was to depressurize the system...translation: open the gas cap and let the "woosh" occur.
I also clamped down the hose leading from the tank with a pair of vice grips to be sure. I only lost a few ounces of fuel during the installation.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car