How simply is it to purge the fuel system on a 2013 Chevrolet Z71 diesel 2500?

You have to drop the gas tank to clean it out properly

Disconect fuel supply line put a hose on long enough te reach a container to catch the nfuel remove the fuel return line and blow moderate air pressure it will push the fuel out,do it until nothing comes outmthen fill the tank complete with fresh diesel fuel,and the soon it reaches 1/8 empty fill tki8s up again ,do it thye many times as you consider necesary. good luck,it wi8ll avoid the removal of the tanks.